Glossory of Physics
 

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[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="blue"]Absorption[/COLOR][/SIZE][/FONT][/B]
It happens when wave passes through a medium and gives up some of its energy.

[FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"][B]Acceleration[/COLOR][/SIZE][/FONT][/B]
Acceleration is the rate of increase of velocity. Acceleration tells you how much faster or slower a moving object gets every second. A negative acceleration is called a deceleration. The SI Unit of acceleration is the metre per second per second (ms-2)

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Acceleration due to Gravity[/COLOR][/SIZE][/FONT][/B]

This is the acceleration caused by the gravitational pull of a planet. On Earth, the strength of the acceleration due to gravity is roughly 10 ms-2. The acceleration due to gravity is often given the symbol 'g'.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Accommodation[/COLOR][/SIZE][/FONT][/B]

Accommodation relates to the ability of the eye to change its focal length and so focus on objects at a range of distances. To focus on a close object, the eye lens will be fat (having a short focal length). To focus on a far object, the lens will be pulled into a thin shape having a long focal length. Failure of accommodation gives rise to long-sightedness and short-sightedness.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Activity[/COLOR][/SIZE][/FONT][/B]

The activity of a sample of radioactive material is the number of disintegrations per second taking place in that particular sample. The SI unit of activity is the becquerel (Bq).

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Aerodynamic[/COLOR][/SIZE][/FONT][/B]

Aerodynamic objects have minimal air resistance. This means that they can move at greater speed through the air. Remember that as objects go faster the aerodynamic drag increases. Therefore, an aerodynamic object will be able to travel faster than a non-aerodynamic one!

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Alpha (a) Radiation[/COLOR][/SIZE][/FONT][/B]

a (alpha) radiation consists of slow moving helium nuclei. These nuclei are released during the disintegration of an unstable nucleus. a radiation will be stopped by a few centimetres of air, or a sheet of paper. It is a strongly ionising radiation, due in part to its relatively large mass - it is about 8000 times as massive as the electrons in b radiation! The helium nuclei are positively charged.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Alternating Current (a.c.)[/COLOR][/SIZE][/FONT][/B]

Electrical current continually changes direction in an a.c. power supply (as opposed to direct current (d.c.))


[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Alternator[/COLOR][/SIZE][/FONT][/B]

This is a device for generating a.c. electricity. It consists of rotor coils (with a d.c. supply) and stator coils which produce the a.c. electricity.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Ampere[/COLOR][/SIZE][/FONT][/B]

The ampere is the SI unit of electrical current. At a simple level it can be defined as the number of coulombs of electrical charge flowing per second.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Amplifier[/COLOR][/SIZE][/FONT][/B]

An amplifier is a component of an electronic system, such as a radio or TV which makes all the input signals louder. Ideally, an amplifier will increase the amplitude of all input signals by the same factor. Amplifiers require a power supply which can be battery or mains. The voltage gain or the power gain can be used to describe how much amplification is taking place.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Amplitude [/COLOR][/SIZE][/FONT][/B]

This is the height of a wave, measured vertically from the centre line to a crest or a trough. The SI unit is the metre, although in some contexts amplitudes may be given in volts.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Amplitude Modulation [/COLOR][/SIZE][/FONT][/B]

Amplitude modulation refers to the changing of the amplitude of a radio-frequency or microwave frequency carrier wave. The other method of modulation is called frequency modulation.


[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Analogue[/COLOR][/SIZE][/FONT][/B]

Analogue signals should be compared with digital signals. Analogue signals are continuous. As an example, a microphone is an analogue input device. This is because it can produce a range of voltage levels.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]AND Gate[/COLOR][/SIZE][/FONT][/B]

An AND gate is a logical device. It usually takes two inputs (although more are possible) and produces only one output. The logic state of the output depends on the logic state of the inputs.


[FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"][B]Angle of Incidence [/COLOR][/SIZE][/FONT][/B]

The angle between the normal line and a ray or wave incident to a surface.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Angular magnification[/COLOR][/SIZE][/FONT][/B]
The factor by which an image's apparent angular size is increased (or decreased). Cf. magnification.
[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]
Angular momentum [/COLOR][/SIZE][/FONT][/B]
A measure of rotational motion; a conserved quantity for a closed system.

[FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"][B]Angle of Reflection [/COLOR][/SIZE][/FONT][/B]

The angle between the normal line and a ray or wave reflected from a surface.


[FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"][B]Asteroid[/COLOR][/SIZE][/FONT][/B]

An asteriod is a lump of rock which orbits around the sun. (The biggest asteroids are about 100km across, although many are 1km or less across. Asteroids orbit the Sun in the asteroid belt, between the orbits of Mars and Jupiter.)

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Atom[/COLOR][/SIZE][/FONT][/B]

The basic unit of one of the chemical elements.

[FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"][B]Average Speed[/COLOR][/SIZE][/FONT][/B]

The average speed of an object is defined as the distance traveled divided by the time elapsed.

Remember that average speed is different from instantaneous speed.

[FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"][B]Audio Wave[/COLOR][/SIZE][/FONT][/B]

A sound wave, but usually in the context of modulation and radio transmission


[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Axis[/COLOR][/SIZE][/FONT][/B]
An arbitrarily chosen point used in the definition of angular momentum. Any object whose direction changes relative to the axis is considered to have angular momentum. No matter what axis is chosen, the angular momentum of a closed system is conserved.

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[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Background Radiation[/COLOR][/SIZE][/FONT][/B]

Background radiation is the radiation which occurs naturally in the rocks, air and water around us.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Battery[/COLOR][/SIZE][/FONT][/B]
A battery is a number (or battery) of cells, connected in series with the positive terminal of one cell connected to the negative of the next. Batteries provide a d.c.(direct current) source of electrical energy.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Beam[/COLOR][/SIZE][/FONT][/B]

The particle stream produced by an accelerator usually clustered in bunches.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]b (beta) radiation[/COLOR][/SIZE][/FONT][/B]

b (beta) radiation consists of fast moving electrons. These electrons are produced as a result of transitions that take place in unstable nuclei. b radiation can be stopped by a few millimetres of aluminium. It is an ionising radiation, not as strongly ionising as a (alpha) radiation.


[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Big-bang Theory[/COLOR][/SIZE][/FONT][/B]

The 'big-bang theory' of cosmology tries to explain the origin of the universe as an explosive event, where space, time and matter came into being.


[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Black Hole[/COLOR][/SIZE][/FONT][/B]

A collapsed star from which no light can escape, due to the intense gravitational field.


[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Block Diagram[/COLOR][/SIZE][/FONT][/B]

In electronics, a block diagram provides a simple way of analysing how a system works. Block diagrams don't show details of how components work, but simply show how information or signals should travel through the system. They are usually drawn using rectangles and arrows.

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[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]
Capacitor [/COLOR][/SIZE][/FONT][/B]

A capacitor is a device which can store electrical charge. Capacitors are often used to introduce a time delay in electronic circuits. The SI unit of capacitance is the farad.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Carrier Wave[/COLOR][/SIZE][/FONT][/B]

Carrier waves are used to carry information from transmitter to receiver. Thecarrier wave will be radio or microwave frequency. There are two methods of using the carrier wave to carry information - amplitude modulation and frequency modulation. In radio transmissions for example, the carrier is of a much higher frequency than the audio wave which is to be transmitted. The higher the frequency of the carrier, the higher the quality of the transmitted signal.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Cathode rays [/COLOR][/SIZE][/FONT][/B]

Negatively charged particles (electrons) that are emitted from a negative terminal in an evacuated glass tube.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Cell [/COLOR][/SIZE][/FONT][/B]

In electricity, a cell is a source of d.c. electricity. A cell can be made using two different metals inserted into a salt solution, for example. The metals react with the salt solution at different rates and in so doing, generate a small electrical current. Many cells can be combined to produce a battery of cells.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]
Celsius scale of temperature[/COLOR][/SIZE][/FONT][/B]

In the celsius scale of temperature, the ice-point is taken as taken as the lower fixed point (0 deg C ) and the steam-point is taken as the upper fixed point (100 deg C). The interval between the ice point and steam point is divided into 100 equal divisions. Thus, the unit division on this scale is 1degC. This scale was earlier called the centigrade scale. 1 deg C = 9/5 deg F.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Center of mass[/COLOR][/SIZE][/FONT][/B]

The balance point of an object.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Centigrade [/COLOR][/SIZE][/FONT][/B]

Alternate name for the Celsius scale.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Centrifugal force [/COLOR][/SIZE][/FONT][/B]

An apparent outward force on an object following a circular path that. This force is a consequence of the third law of motion.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Centripetal force [/COLOR][/SIZE][/FONT][/B]

The force required to pull an object out of its natural straight-line path and into a circular path.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Chain reaction[/COLOR][/SIZE][/FONT][/B]

A self-sustaining reaction where some of the products are able to produce more reactions of the same kind; in a nuclear chain reaction neutrons are the products that produce more nuclear reactions in a self-sustaining series

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Charge[/COLOR][/SIZE][/FONT][/B]

A numerical rating of how strongly an object participates in electrical forces.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Chemical Potential Energy[/COLOR][/SIZE][/FONT][/B]

Chemical energy is a form of potential energy because it is stored energy. Energy stored in food, torch batteries and explosives like dynamite is all chemical energy. Chemical energy is released in a chemical reaction (like combustion of explosives or respiration in plant and animal cells).

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Circuit[/COLOR][/SIZE][/FONT][/B]

An electrical device in which charge can come back to its starting point and be recycled rather than getting stuck in a dead end.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Circular Motion[/COLOR][/SIZE][/FONT][/B]

The motion of a body along a circular path is called circular motion.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Clock Pulse Generator[/COLOR][/SIZE][/FONT][/B]

A simple circuit using a capacitor, resistor and transistor. The circuit generates 'clock pulses' - simply a regular sequence of logic LO and logic HI. The capacitor charges and discharges through the resistor. As the capacitor charges to a certain level, the inverter's input goes HI and its output goes LO. This this causes the capacitor to start discharging. When its voltage gets low enough, the inverter output goes back to HI and the cycle starts again.

By increasing the resistance or increasing the capacitance, the pulses can be generated more slowly.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Coefficient of cubical expansion [/COLOR][/SIZE][/FONT][/B]

The increase in volume of a substance per unit original volume per degree rise in temperature is called its coefficient of cubical expansion. The SI unit of coefficient of cubical expansion is K-1.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Coefficient of linear expansion[/COLOR][/SIZE][/FONT][/B]

The increase in length per unit original length per degree rise in temperature is called the coefficient of linear expansion. The SI unit of the coefficient of linear expansion is K-1.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Coherent[/COLOR][/SIZE][/FONT][/B]

A light wave whose parts are all in phase with each other.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Collision[/COLOR][/SIZE][/FONT][/B]

An interaction between moving objects that lasts for a certain time.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Comet[/COLOR][/SIZE][/FONT][/B]

A comet is a small body orbiting our Sun, usually at great distance from Earth and with a highly elliptical orbit. They are composed of 'ices' and dust. As a comet approaches the inner solar system, the heat of the Sun vapourises volatile material from the surface and pushes the material directly away from the Sun. This gives rise to the 'ion tail', usually a ghostly blue colour and quite straight, it always points directly away from the Sun and has nothing to do with the direction of motion of the comet. A second tail exists, usually white and curved. This is dust which falls off the comet and is left in track of its orbit.


[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Component[/COLOR][/SIZE][/FONT][/B]

The part of a velocity, acceleration, or force that is along one particular coordinate axis.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Compression[/COLOR][/SIZE][/FONT][/B]

A part of a longitudinal wave in which the density of the particles of the medium is higher than the normal density is called a compression.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Compressive stress[/COLOR][/SIZE][/FONT][/B]

A force that tends to compress the surface as the earth's plates move into each other.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Concave[/COLOR][/SIZE][/FONT][/B]

Describes a surface that is hollowed out like a cave.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Condensation (sound)[/COLOR][/SIZE][/FONT][/B]

A compression of gas molecules; a pulse of increased density and pressure that moves through the air at the speed of sound.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Condensation (water vapor)[/COLOR][/SIZE][/FONT][/B]

Where more vapor or gas molecules are returning to the liquid state than are evaporating.

[FONT="Comic Sans MS"][B][SIZE="4"][COLOR="Blue"]Condensation nuclei [/COLOR][/SIZE][/B][/FONT]

Tiny particles such as tiny dust, smoke, soot, and salt crystals that are suspended in the air on which water condenses condensation point the temperature at which a gas or vapor changes back to a liquid.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Condensation point[/COLOR][/SIZE][/FONT][/B]

The temperature at which a gas or vapor changes back to a liquid.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Conductor[/COLOR][/SIZE][/FONT][/B]

A material that allows electricity to flow easily through it. Copper, for example is a good conductor. Good conductors have a very low resistance. See also insulators and semi-conductors.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Conduction [/COLOR][/SIZE][/FONT][/B]

The transfer of heat from a region of higher temperature to a region of lower temperature by increased kinetic energy moving from molecule to molecule.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Constructive interference [/COLOR][/SIZE][/FONT][/B]

The condition in which two waves arriving at the same place, at the same time and in phase, add amplitudes to create a new wave.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Consumer Unit[/COLOR][/SIZE][/FONT][/B]

Commonly known as the fusebox, the consumer unit is the part of the meter board which separates the incoming electrical supply into the various lighting and ring main circuits. Each of these circuits is protected by either a fuse or miniature circuit breaker (MCB).

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Control rods[/COLOR][/SIZE][/FONT][/B]

Rods inserted between fuel rods in a nuclear reactor to absorb neutrons and thus control the rate of the nuclear chain reaction.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Convection [/COLOR][/SIZE][/FONT][/B]

The transfer of heat from one place to another by the motion of a gas or a liquid across the heated surface.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Convex[/COLOR][/SIZE][/FONT][/B]

Describes a surface that bulges outward.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Conventional current[/COLOR][/SIZE][/FONT][/B]

Opposite to electron current-that is, considers an electric current to consist of a drift of positive charges that flow from the positive terminal to the negative terminal of a battery.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Coulomb [/COLOR][/SIZE][/FONT][/B]

Unit used to measure quantity of electric charge; equivalent to the charge resulting from the transfer of 6.24 billion particles such as the electron.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Coulomb's law[/COLOR][/SIZE][/FONT][/B]

Relationship between charge, distance, and magnitude of the electrical force between two bodies.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Covalent bond[/COLOR][/SIZE][/FONT][/B]

A chemical bond formed by the sharing of a pair of electrons.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Covalent compound[/COLOR][/SIZE][/FONT][/B]

Chemical compound held together by a covalent bond or bonds.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Crest[/COLOR][/SIZE][/FONT][/B]

The point of maximum positive displacement on a transverse wave is called a crest.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Critical angle [/COLOR][/SIZE][/FONT][/B]

Limit to the angle of incidence when all light rays are reflected internally.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Critical mass [/COLOR][/SIZE][/FONT][/B]

Mass of fissionable material needed to sustain a chain reaction.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Current[/COLOR][/SIZE][/FONT][/B]

Electrical current is the rate of flow of electrical charge round a circuit. It is measured in amperes and should be measured in series with an ammeter.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Curvilinear Motion[/COLOR][/SIZE][/FONT][/B]

The motion of a body along a curved path is called curvilinear motion.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Cycle [/COLOR][/SIZE][/FONT][/B]

A complete vibration.

[B][CENTER][FONT="Comic Sans MS"][SIZE="6"][COLOR="Blue"]D[/COLOR][/SIZE][/FONT][/CENTER][/B]


[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Damping[/COLOR][/SIZE][/FONT][/B]

The dissipation of a vibration's energy into heat energy, or the frictional force that causes the loss of energy.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Deceleration[/COLOR][/SIZE][/FONT][/B]

Deceleration basically means slowing down - reducing speed. A negative answer for an acceleration would actually be a deceleration. Like acceleration, deceleration is also measured in ms-2.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Decibel (dB) Scale[/COLOR][/SIZE][/FONT][/B]

The decibel scale is used to measure the volume (intensity or loudness) of sound. The abbreviation for this unit is dB.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Decoder[/COLOR][/SIZE][/FONT][/B]

The decoder section of a radio essentially removes the carrier wave from the modulated signal, leaving only the audio wave which is then amplified. In TVs there are two separate decoders - one for the picture and one for the sound.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Deflection Plates[/COLOR][/SIZE][/FONT][/B]

Deflection plates are used to direct the electron beam to all parts of the cathode ray tube of an oscilloscope. There are two sets of plates, one set for controlling horizontal movement of the beam and the other set for vertical movement. Each set of plates controls the beam by having a certain voltage applied across the plates.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Destructive interference[/COLOR][/SIZE][/FONT][/B]

The condition in which two waves arriving at the same point at the same time out of phase add amplitudes to create zero total disturbance.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Dew point temperature[/COLOR][/SIZE][/FONT][/B]

The temperature at which condensation begins.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Dew[/COLOR][/SIZE][/FONT][/B]

Condensation of water vapor into droplets of liquid on surfaces.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Diffraction[/COLOR][/SIZE][/FONT][/B]

Diffraction is a wave phenomenon - i.e. all types of wave can diffract. Diffraction means the bending of wave (change in direction) and it occurs whenever a wave passes near to an obstacle. Longer wavelength waves diffract through a greater angle than shorter wavelength waves.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Diffuse reflection[/COLOR][/SIZE][/FONT][/B]

Light rays reflected in many random directions, as opposed to the parallel rays reflected from a perfectly smooth surface such as a mirror.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Digital[/COLOR][/SIZE][/FONT][/B]

Digital can refer to electronic signals or to components of an electronic system. Digital signals have only two voltage levels, described as 'HI' and 'LO', or 'OFF' and 'ON'. In a real component, 'HI' might be represented by +5V d.c. and 'LO' by 0V d.c. A digital component is one which works with only digital signals. Here are some examples of digital components: LED (output), photodiode (input), switch (input).

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Diode [/COLOR][/SIZE][/FONT][/B]

A diode is a semi-conductor device. Diodes will allow current to pass through them in only one direction.

[IMG]http://www.users.zetnet.co.uk/computing/MainPage/SecDepts/Physics/Resources/Glossary/LED.gif[/IMG]



[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Direct current[/COLOR][/SIZE][/FONT][/B]

An electrical current that always moves in one direction.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Direct proportion[/COLOR][/SIZE][/FONT][/B]

When two variables increase or decrease together in the same ratio (at the same rate).

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Dispersion [/COLOR][/SIZE][/FONT][/B]

The effect of spreading colors of light into a spectrum with a material that has an index of refraction that varies with wavelength.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Displacement[/COLOR][/SIZE][/FONT][/B]

The change in the position of an object in a particular direction is called displacement. Displacement may also be defined as the shortest distance between the initial and final position of a moving body. It is a vector quantity.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Distance[/COLOR][/SIZE][/FONT][/B]

The actual length of the path traveled by a body irrespective of the direction is called the distance traveled. It is a scalar quantity.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Doppler effect[/COLOR][/SIZE][/FONT][/B]

An apparent shift in the frequency of sound or light due to relative motion between the source of the sound or light and the observer.


[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Dose Equivalent[/COLOR][/SIZE][/FONT][/B]

This is the biological risk due to exposure to radiation. The SI unit of dose equivalent is the sievert (Sv).

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Double Insulation[/COLOR][/SIZE][/FONT][/B]

An electrical appliance which is double insulated does not have an earth wire fitted. The appliance is designed in such a way that the electrical parts can never come into contact with the outer casing of the device. Common double insulated appliances are hair dryers, radios and cassette players.

A wet double insulated appliance is exceptionally dangerous - water is a good conductor of electricity and will easily reach the live electrical components within the case. Any human user touching the casing will then receive an electric shock. It is important to note that the human conductivity is increased when hands are wet, allowing a greater current to flow through the casualty.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Drag[/COLOR][/SIZE][/FONT][/B]

Drag is a type of friction force usually associated with movement through a fluid like air or water. Drag forces generally increase at high speeds.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Driving force[/COLOR][/SIZE][/FONT][/B]

An external force that pumps energy into a vibrating system.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Dynamo[/COLOR][/SIZE][/FONT][/B]

A device (a traducer) which converts kinetic energy into electrical energy. Dynamos are often used to produce a.c. electricity on a push-bike. Unlike a full-blown generator, the rotor coil is replaced with rotating permanent magnets. These magnets rotate near to the stator coil, (wrapped around a soft iron core) and cause a small current to flow (via electromagnetic induction).

[B][CENTER][FONT="Comic Sans MS"][SIZE="6"][COLOR="Blue"]E[/COLOR][/SIZE][/FONT][/CENTER][/B]



[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Echo [/COLOR][/SIZE][/FONT][/B]

A reflected sound that can be distinguished from the original sound, which usually arrives 0.1 sec or more after the original sound.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Efficiency[/COLOR][/SIZE][/FONT][/B]

Efficiency is defined as 'Useful Energy Out' / 'Total Energy In'. It is a fraction, sometimes written as a percentage.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Elastic strain [/COLOR][/SIZE][/FONT][/B]

An adjustment to stress in which materials recover their original shape after a stress is released.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Electric circuit [/COLOR][/SIZE][/FONT][/B]

Consists of a voltage source that maintains an electrical potential, a continuous conducting path for a current to follow, and a device where work is done by the electrical potential; a switch in the circuit is used to complete or interrupt the conducting path.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Electric current [/COLOR][/SIZE][/FONT][/B]

Electric current is the flow (movement) of electric charge. The SI unit of electric current is the Ampere (A), which is equal to a flow of one Coulomb of charge per second. Electric current is measured using an ammeter.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Electric dipole [/COLOR][/SIZE][/FONT][/B]

An object that has an imbalance between positive charge on one side and negative charge on the other; an object that will experience a torque in an electric field.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Electric field lines[/COLOR][/SIZE][/FONT][/B]

A map of an electric field representing the direction of the force that a test charge would experience; the direction of an electric field shown by lines of force.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Electric generator [/COLOR][/SIZE][/FONT][/B]

A mechanical device that uses wire loops rotating in a magnetic field to produce electromagnetic induction in order to generate electricity.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Electric potential energy[/COLOR][/SIZE][/FONT][/B]

Potential energy due to the position of a charge near other charges.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Electrical conductors[/COLOR][/SIZE][/FONT][/B]

Materials that have electrons that are free to move throughout the material; for example, metals.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Electrical energy[/COLOR][/SIZE][/FONT][/B]

A form of energy from electromagnetic interactions; one of five forms of energy-mechanical, chemical, radiant, electrical, and nuclear.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Electrical force[/COLOR][/SIZE][/FONT][/B]

A fundamental force that results from the interaction of electrical charge and is billions and billions of times stronger than the gravitational force.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Electrical insulators[/COLOR][/SIZE][/FONT][/B]

Electrical nonconductors, or materials that obstruct the flow of electric current.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Electrical nonconductors[/COLOR][/SIZE][/FONT][/B]

Materials that have electrons that are not moved easily within the material-for example, rubber; electrical nonconductors are also called electrical insulators.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Electrical resistance[/COLOR][/SIZE][/FONT][/B]

The property of opposing or reducing electric current.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Electrolyte [/COLOR][/SIZE][/FONT][/B]

Water solution of ionic substances that conducts an electric current.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Electromagnet[/COLOR][/SIZE][/FONT][/B]

An electromagnet is a solenoid with an iron core inserted into it. If a current flows in the coil, a magnetic field is generated. All the randomly oriented domains of the iron core then align in the presence of the field of the solenoid. Thus, the core greatly enhances the strength of the electromagnet.

[IMG]http://www.bbc.co.uk/schools/ks3bitesize/science/images/sci_dia_79.gif[/IMG]


[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Electromagnetic induction[/COLOR][/SIZE][/FONT][/B]

Process in which current is induced by moving a loop of wire in a magnetic field or by changing the magnetic field.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Electromagnetic Spectrum[/COLOR][/SIZE][/FONT][/B]

This includes Gamma, X-rays, Ultraviolet, Visible, Infra-red, Microwave and Radio - in order of increasing wavelength.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Electromagnetic waves[/COLOR][/SIZE][/FONT][/B]

The waves which are due to oscillating electrical and magnetic fields and do not need any material medium for their propagation are called electromagnetic waves. These waves can, however, travel through material medium also. Light waves, radio waves are examples of electromagnetic waves. All electromagnetic waves travel in vacuum with a speed of 3×10 8 m/s.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Electron configuration [/COLOR][/SIZE][/FONT][/B]

The arrangement of electrons in orbits and sub-orbits about the nucleus of an atom.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Electron current [/COLOR][/SIZE][/FONT][/B]

Opposite to conventional current; that is, considers electric current to consist of a drift of negative charges that flows from the negative terminal to the positive terminal of a battery.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Electron pair [/COLOR][/SIZE][/FONT][/B]

A pair of electrons with different spin quantum numbers that may occupy an orbital.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Electron volt[/COLOR][/SIZE][/FONT][/B]

The energy gained by an electron moving across a potential difference of one volt; equivalent to 1.60 x 10^-19 Joules.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Electron[/COLOR][/SIZE][/FONT][/B]

Electrons are sub-atomic particles. They carry a negative electrical charge (qe=-1.602 x 10-19 C).
They have a mass of me = 9.110 x 10-31 kg.

Beams of electrons are used in TV sets where they are called cathode rays.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Electro negativity. [/COLOR][/SIZE][/FONT][/B]

The comparative ability of atoms of an element to attract bonding electrons.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Electronic System[/COLOR][/SIZE][/FONT][/B]

An electronic system can simply be considered as consisting of three parts: input, process and output. Input devices include microphones and LDRs, thermistors and switches. Process sections can be made from one or more transistors, perhaps built into logic gates or computer chips. The output section will consist of one or more output devices, for example, a buzzer, LED, lamp, CRT.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Electrostatic charge [/COLOR][/SIZE][/FONT][/B]

An accumulated electric charge on an object from a surplus or deficiency of electrons.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Element [/COLOR][/SIZE][/FONT][/B]

A pure chemical substance that cannot be broken down into anything simpler by chemical or physical means.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Energy [/COLOR][/SIZE][/FONT][/B]

The capacity of a body to do work is called its energy. Energy is a scalar quantity. The SI unit of energy is Joule.Energy can not be created or destroyed, but can be changed from one form to another.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Escape Velocity[/COLOR][/SIZE][/FONT][/B]

The minimum velocity with which an object must be thrown upwards so as to overcome the gravitational pull and escape into space, is called escape velocity (V esc ). The escape velocity depends upon the mass and radius of the planet/star. It does not depend upon the mass of the body thrown up.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Equilibrium[/COLOR][/SIZE][/FONT][/B]

A state in which an object's momentum and angular momentum are constant.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Evaporation[/COLOR][/SIZE][/FONT][/B]

Process of more molecules leaving a liquid for the gaseous state than returning from the gas to the liquid. It can occur at any given temperature from the surface of a liquid. Evaporation takes place only from the surface of the liquid. Evaporation causes cooling. Evaporation is faster if the surface of the liquid is large, the temperature is higher and the surrounding atmosphere does not contain a large amount of vapor of the liquid.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Eyepiece Lens[/COLOR][/SIZE][/FONT][/B]

The lens on a telescope (or microscope) which the observer places his or her eye next to. The eyepiece's sole funciton is to magnify the image.

[B][CENTER][FONT="Comic Sans MS"][SIZE="6"][COLOR="Blue"]F[/COLOR][/SIZE][/FONT][/CENTER][/B]



[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Farad [/COLOR][/SIZE][/FONT][/B]

The farad (F) is the SI Unit of capacitance.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Fahrenheit scale of temperature[/COLOR][/SIZE][/FONT][/B]

On the Fahrenheit scale, the ice point, the ice point (lower fixed point) is taken as 32? F and the steam point (upper fixed point) is taken as 212 deg F. The interval between these two points is divided into 180 equal divisions. Thus, unit division on the Fahrenheit scale is 1deg F. The temperatures on the Celsius scale and the Fahrenheit scale are related by the relationship, C/100 = (F - 32) / 180. The temperature of a normal healthy person is 37 deg C or 98.6 deg F.


[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Fibrescope[/COLOR][/SIZE][/FONT][/B]

Fibrescope are sometimes called endoscopes. A flexible fiber-optic instrument used to view an object or area, such as a body cavity, that would otherwise be inaccessible.


[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Field[/COLOR][/SIZE][/FONT][/B]

A property of a point in space describing the forces that would be exerted on a particle if it was there.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Filament Lamp[/COLOR][/SIZE][/FONT][/B]

These lamps rely on an incandescent metal filament to produce light. The interior of the lamp is filled with an inert gas in order to stop the filament from corroding. An electrical current, passed through the filament makes it extremely hot. When sufficiently hot, the filament itself will emit light radiation. Tungsten metal is chosen for the filament due to its high melting point of about 3956 Celsius.


[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]First law of motion [/COLOR][/SIZE][/FONT][/B]

Every object remains at rest or in a state of uniform straight-line motion unless acted on by an unbalanced force.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Fission Process[/COLOR][/SIZE][/FONT][/B]

This usually refers to nuclear fission, where an atomic nucleus splits apart into smaller pieces. Fission should not be confused with fusion. When a heavy, unstable nucleus undergoes fission, energy is released as heat. In nuclear power stations, uranium is often used as the fissile material, where a nuclear chain reaction is controlled to release energy.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Flex [/COLOR][/SIZE][/FONT][/B]

The flex allows electrical current to flow into domestic appliances from the mains socket. The flex should be correctly wired to a plug.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Fluids[/COLOR][/SIZE][/FONT][/B]

Matter that has the ability to flow or be poured; the individual molecules of a fluid are able to move, rolling over or by one another.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Fluid friction[/COLOR][/SIZE][/FONT][/B]

A friction force in which at least one of the object is a fluid (i.e. either a gas or a liquid).

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Fluorescent Lamps[/COLOR][/SIZE][/FONT][/B]

These lamps produce light by passing electrical current through a mercury vapour at low pressure. The electrical current excites ("energises") the electrons of the mercury atoms. These electrons quickly give up their energy as light. The light which is produced is invisible ultra-violet and would be useless. To get round this problem, the inside of the tube is coated with fluorescent paint, which converts U.V. light to visible light.
Fluorescent lamps are more efficient than filament lamps as they waste less energy as heat.


[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Focal Length[/COLOR][/SIZE][/FONT][/B]

The focal length of lens is measured in meters. It is the distance from the centre of the lens to the point at which rays passing through the lens meet (i.e. focus). It is related to lens power.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Force[/COLOR][/SIZE][/FONT][/B]

Forces can cause an object to speed up, slow down, change direction or change shape (if they are unbalanced). Forces are either push forces or pull forces. Force is a vector quantity.The SI unit of force is the newton,denoted by N.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Force of gravitation [/COLOR][/SIZE][/FONT][/B]

The force with which two objects attract each other by virtue of their masses is called the force of gravitation. The force of attraction acts even if the two objects are not connected to each other. It is an action-at-a-distance force.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Fossil Fuel [/COLOR][/SIZE][/FONT][/B]

Fossil fuels are coal, oil and gas. They are non-renewable resources. Fossil fuels come from ancient remains of plants and animals, compressed and heated over many millenia. The combustion of fossil fuels is now (nearly) universally accepted as causing global warming. They are well known to produce acid rain. Most of the world's energy is still produced from fossil fuel.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Fracture strain[/COLOR][/SIZE][/FONT][/B]

An adjustment to stress in which materials crack or break as a result of the stress.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Free fall [/COLOR][/SIZE][/FONT][/B]

The motion of a body towards the earth when no other force except the force of gravity acts on it is called free fall. All freely falling bodies are weightless.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Freezing point[/COLOR][/SIZE][/FONT][/B]

The temperature at which a phase change of liquid to solid takes place; the same temperature as the melting point for a given substance.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Frequency[/COLOR][/SIZE][/FONT][/B]

The frequency of a regular event is the number of times the event occurs in a given time.The SI unit of frequency is the hertz (Hz) (equivalent to 'per second' or s-1).

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Frequency (of waves) [/COLOR][/SIZE][/FONT][/B]

The number of waves produced per second is called its frequency.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Frequency (of oscillations) [/COLOR][/SIZE][/FONT][/B]

The number of oscillations made by an oscillating body per second is called the frequency.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Frequency Modulation[/COLOR][/SIZE][/FONT][/B]

Frequency modulation refers to the changing of the frequency of a radio-frequency or microwave frequency carrier wave. The other method of modulation is called amplitude modulation.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Friction[/COLOR][/SIZE][/FONT][/B]

Friction is a force which tends to make moving objects slow down. Friction also prevents objects from slipping over one another. Friction due to fluid flow is called drag.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Fridge [/COLOR][/SIZE][/FONT][/B]

A fridge is an example of a heat pump. It extracts heat energy from inside the fridge cabinet and releases it into the room. The basic principle relies on the latent heat of vaporisation of a coolant liquid. The coolant is evaporated within the pipes inside the cabinet - the heat required for this is taken from the cabinet itself, with the result that the cabinet becomes cooler.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Fuel rod [/COLOR][/SIZE][/FONT][/B]

Long zirconium alloy tubes containing fissionable material for use in a nuclear reactor.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Fundamental charge[/COLOR][/SIZE][/FONT][/B]

Smallest common charge known; the magnitude of the charge of an electron and a proton, which is 1.60 x 10^-19 coulomb.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Fundamental frequency[/COLOR][/SIZE][/FONT][/B]

The lowest frequency (longest wavelength) that can set up standing waves in an air column or on a string.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Fundamental properties[/COLOR][/SIZE][/FONT][/B]

A property that cannot be defined in simpler terms other than to describe how it is measured; the fundamental properties are length, mass, time, and charge.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Fuse[/COLOR][/SIZE][/FONT][/B]

A fuse, where fitted, is designed to protect the flex (and not the appliance) from current overload and the associated risk of fire. The fuse rating should always be less than that of the flex which it is protecting. This will make sure that it blows before the flex melts. If the fuse in the plug blows, it is likely to be because of a fault in the appliance which is drawing too much current.
The fuse (and switch) should always be connected to the live wire in a plug.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Fusion[/COLOR][/SIZE][/FONT][/B]

A nuclear reaction in which two nuclei stick together to form one bigger nucleus.

[B][CENTER][FONT="Comic Sans MS"][SIZE="6"][COLOR="Blue"]G[/COLOR][/SIZE][/FONT][/CENTER][/B]


[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]g [/COLOR][/SIZE][/FONT][/B]

Symbol representing the acceleration of an object in free fall due to the force of gravity; its magnitude is 9.80 m/sec^2 (32.0 ft/sec^2).

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Galaxy[/COLOR][/SIZE][/FONT][/B]

A grouping of about approximately 100 billion stars, held together by their own gravity. We live in the Milky Way galaxy.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Gamma (g) Radiation[/COLOR][/SIZE][/FONT][/B]

g (gamma) radiation is high frequency electromagnetic radiation. It is a part of the electromagnetic spectrum. Gamma radiation carries no mass, no charge, travels at the speed of light. (It can be thought of as being made of particles called photons or as being a wave). It can be stopped by several centimetres of lead or a few metres of concrete. Gamma radiation is an ionising radiation, but is not as strongly ionising as a radiation. It is released during the disintegration of an unstable nucleus.
For the purposes of treating cancer, medical gamma rays from cobalt-60 are used.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Gamma Camera[/COLOR][/SIZE][/FONT][/B]

This is a device used to detect the gamma radiation from a patient during an examination using a radioactive tracer. Since gamma radiation passes straight through most materials, it is not possible to build a camera with glass lenses or mirrors. Instead an array of holes drilled in a thick layer of lead is placed between the actual gamma detectors and the patient. This allows an image to be built up. Scintillation counters are used to detect the radiation after it has passed through the holes in the commutator.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Gases[/COLOR][/SIZE][/FONT][/B]

A phase of matter composed of molecules that are relatively far apart moving freely in a constant, random motion and have weak cohesive forces acting between them, resulting in the characteristic indefinite shape and indefinite volume of a gas.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Gas Discharge Lamps[/COLOR][/SIZE][/FONT][/B]

These lamps produce light by passing electrical current through a gas at low pressure. The electrical current excites ("energises") the electrons of the atoms in the gas. These electrons quickly give up their energy as light. Sodium is often used (in street lights) or an inert gas for colourful advertising lights.
Discharge lamps are more efficient than filament lamps as they waste less energy as heat.


[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Geiger-Muller tube[/COLOR][/SIZE][/FONT][/B]

This is a device used to detect the presence of radiation. It relies on ionisation to produce tiny bursts of current which can be counted by a rate meter.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Geostationary[/COLOR][/SIZE][/FONT][/B]

'Geostationary' refers to a satellite of planet Earth. Such a satellite will appear to hover above the surface of the Earth, since it is placed in an orbit with a period of 24 hours.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Geothermal Energy[/COLOR][/SIZE][/FONT][/B]

This is a renewable energy resource, unlike fossil fuels. In some parts of the world, hot subsurface rock heats water which reaches the surface and can be used for heating or electrical power generation.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Generator[/COLOR][/SIZE][/FONT][/B]

A machine which uses motion to produce electrical energy. Sometimes called an alternator. A generator is like a dynamo, but with the permanent rotor magnets replaced with (d.c) rotor coils (electromagnets). The stator coils have an a.c. induced within them.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Gold Grain[/COLOR][/SIZE][/FONT][/B]

Radioactive gold grains are used in the treatment of cancer. Gold (which is unreactive) doped with radioactive (gamma emitting) nuclei is implanted in a patient, near or in a tumour. The radiation will destroy or damage cells near the grain. The radioactive material chosen will have a short half-life so that the grain's activity level will drop to background levels after several days.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Gram-atomic weight[/COLOR][/SIZE][/FONT][/B]

The mass in grams of one mole of an element that is numerically equal to its atomic weight.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Gram-formula weight.[/COLOR][/SIZE][/FONT][/B]

The mass in grams of one mole of a compound that is numerically equal to its formula weight.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Gram-molecular weight.[/COLOR][/SIZE][/FONT][/B]

The gram-formula weight of a molecular compound.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Gravity[/COLOR][/SIZE][/FONT][/B]

A general term for the phenomenon of attraction between things having mass. The attraction between our planet and a human-sized object causes the object to fall.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Gravitational constant G[/COLOR][/SIZE][/FONT][/B]

The constant G which appears in the equation for Newton's law of gravitation is called the universal constant of gravitation or the gravitational constant. Numerically it is equal to the force of gravitation, which acts between two bodies of mass 1kg each separated by a distance of 1m. The value of G is 6.67×10-11 Nm²/kg².

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Gravitational Field [/COLOR][/SIZE][/FONT][/B]

The Earth generates a gravitational field which attracts all other masses. It is a called a force field - the word field means that the force changes as you move away from the surface of the Earth (in fact the force becomes steadily less as you move away from the surface of the Earth). It is the combined mass of all particles on Earth which cause the Earth's gravitational field. The strength of the field is measured in Nkg-1.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Gravitational Potential Energy[/COLOR][/SIZE][/FONT][/B]

Gravitational potential energy is energy an object possesses because of its position in a gravitational field.

If a mass is lifted up then its potential energy is given as follows:

Ep = mgh

Ep is the potential energy

m is the mass in kilograms

g is the strength of the gravitational field (10ms-2 on Earth)

h is the height through which the object is lifted

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Greenhouse effect[/COLOR][/SIZE][/FONT][/B]

The process of increasing the temperature of the lower parts of the atmosphere through redirecting energy back toward the surface; the absorption and reemission of infrared radiation by carbon dioxide, water vapor, and a few other gases in the atmosphere.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Ground state[/COLOR][/SIZE][/FONT][/B]

Energy state of an atom with electrons at the lowest energy state possible for that atom.

[B][CENTER][FONT="Comic Sans MS"][SIZE="6"][COLOR="Blue"]H [/COLOR][/SIZE][/FONT][/CENTER][/B]


[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Half-life [/COLOR][/SIZE][/FONT][/B]

The half-life of a radioactive material is the time taken for its activity level to drop by a half. Half-life is measured using any unit of time (seconds, hours).

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Heat[/COLOR][/SIZE][/FONT][/B]

Heat is a form of energy, which makes a body hot or cold. Heat is measured by the temperature-effect it produces in any material body. The SI unit of heat is Joule( J).

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Heat Energy[/COLOR][/SIZE][/FONT][/B]

Heat is a form of energy and is not to be confused with temperature. There is no such thing as 'cold energy'. At the molecular level, heat energy is transferred from particle to particle by vibration (this is called conduction). A particle vibrating violently can be said to have a lot of heat energy. As well as by conduction, heat can also be transferred by convection or radiation.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Heater[/COLOR][/SIZE][/FONT][/B]

The operation of a bar heater is very similar indeed to a filament lamp. The difference is in the thickness of the 'filament' or element of the heater. Curiously, heaters operate at a lower temperature than lamps, but produce far more heat - as infra-red radiation.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Heat Pump[/COLOR][/SIZE][/FONT][/B]

This is a device which can move heat energy from a colder object to a hotter one, but requiring an external energy source to do it. A fridge is an example of a heat pump. Due to the second law of thermodynamics, a heat pump can never be 100% efficient.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Heat death of the Universe[/COLOR][/SIZE][/FONT][/B]

Time at which no work will be able to be done because all heat energy in the Universe will be evenly distributed (so that no further increase in entropy is possible).

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Heisenberg uncertainty principle [/COLOR][/SIZE][/FONT][/B]

You cannot measure both the exact momentum and the exact position of a subatomic particle at the same time-when the more exact of the two is known, the less certain you are of the value of the other.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Hertz[/COLOR][/SIZE][/FONT][/B]

Unit of frequency; equivalent to one cycle per second.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Horsepower[/COLOR][/SIZE][/FONT][/B]

Measurement of power defined as a power rating of 550 ft-lb/sec.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Hypothesis[/COLOR][/SIZE][/FONT][/B]

A tentative explanation of a phenomenon that is compatible with the data and provides a framework for understanding and describing that phenomenon.






[B][CENTER][FONT="Comic Sans MS"][SIZE="6"][COLOR="Blue"]I[/COLOR][/SIZE][/FONT][/CENTER][/B]


[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Ice-point[/COLOR][/SIZE][/FONT][/B]

It is the melting point of pure melting ice under 1 Atmospheric pressure. The ice point is taken as the lower fixed point ( 0 deg C or 32 deg F ) for temperature scales.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Image[/COLOR][/SIZE][/FONT][/B]

A place where an object appears to be, because the rays diffusely reflected from any given point on the object have been bent so that they come back together and then spread out again from the image point, or spread apart as if they had originated from the image.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Impulse[/COLOR][/SIZE][/FONT][/B]

The impulse acting on a body is equal to the product of the force acting on the body and the time for which it acts. If the force is variable, the impulse is the integral of Fdt from t0 to t1. The impulse of a force acting for a given time interval is equal to change in momentum produced over that interval. J=m(v-u), assuming that the mass m remains constant while the velocity changes from v to u. The SI units of impulse are kg m/s.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Impulsive force[/COLOR][/SIZE][/FONT][/B]

The force which acts on a body for a very short time but produces a large change in the momentum of the body is called an impulsive force.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Incandescent[/COLOR][/SIZE][/FONT][/B]

Matter emitting visible light as a result of high temperature for example, a light bulb, a flame from any burning source, and the sun are all incandescent sources because of high temperature.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Incident ray[/COLOR][/SIZE][/FONT][/B]

Line representing the direction of motion of incoming light approaching a boundary.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Independence[/COLOR][/SIZE][/FONT][/B]

The lack of any relationship between two random events.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Index of refraction[/COLOR][/SIZE][/FONT][/B]

The ratio of the speed of light in a vacuum to the speed of light in a material.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Induction[/COLOR][/SIZE][/FONT][/B]

The production of an electric field by a changing magnetic field, or vice-versa.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Inert [/COLOR][/SIZE][/FONT][/B]

A chemical element is inert if it does not react with anything. Examples are helium, neon, argon, krypton, xenon and radon. Inert gases can be used in filament lamps to protect the filament from destruction due corrosion.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Inertia [/COLOR][/SIZE][/FONT][/B]

The property of matter that causes it to resist any change in its state of rest or of uniform motion. There are three kinds of inertia- inertia of rest, inertia of motion and inertia of direction. The mass of a body is a measure of its inertia.The SI unit for inertia is the kilogram.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Inertial frame[/COLOR][/SIZE][/FONT][/B]

A frame of reference that is not accelerating, one in which Newton's first law is true.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Infrasonic[/COLOR][/SIZE][/FONT][/B]

Sound waves having too low a frequency to be heard by the human ear; sound having a frequency of less than 20 Hz.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Infrared[/COLOR][/SIZE][/FONT][/B]

Infrared radiation is invisible. It is a form of electromagnetic radiation, with a wavelength just longer than that of visible red light. Infrared light is use in telecommunications (via optical fibres). It is used in medicine to diagnose illness (thermograms) and accelerate healing in physiotherapy. Infrared radiation can be thought of as 'heat rays'.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Input Device[/COLOR][/SIZE][/FONT][/B]

The first part of an electronic system, an input device typically processes requests from a human user. For example in a CD player, the 'ON' button and volume controls (potentiometer) are all input devices. Other input devices include switches, thermistors, LDRs, photodiodes.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Instantaneous[/COLOR][/SIZE][/FONT][/B]

This means an event which occurs over a very short (infinitesimal) period of time. It usually refers to speed, i.e. instantaneous speed as opposed to average speed.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Instantaneous Speed[/COLOR][/SIZE][/FONT][/B]

The speed at any particular stage or time during a journey. Instantaneous speed can be calculated by measuring short distances and time intervals.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Insulator[/COLOR][/SIZE][/FONT][/B]

A material which does not usually conduct electricity. Air, for example is an insulator. Insulators have a very high (ideally infinite) resistance. Given a suitably high voltage, insulators can be forced to conduct ,for example lightning during a thunderstorm.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Insulation [/COLOR][/SIZE][/FONT][/B]

A nonconducting material designed to reduce the transfer of energy or electric current between two materials.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Intensity[/COLOR][/SIZE][/FONT][/B]

A measure of the energy carried by a wave.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Interference[/COLOR][/SIZE][/FONT][/B]

Phenomenon of light where the relative phase difference between two light waves produces light or dark spots, a result of light's wavelike nature.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Intermolecular forces[/COLOR][/SIZE][/FONT][/B]

Forces of interaction between molecules.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Internal energy[/COLOR][/SIZE][/FONT][/B]

Sum of all the potential energy and all the kinetic energy of all the molecules of an object.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Invariant[/COLOR][/SIZE][/FONT][/B]

A quantity that does not change when transformed.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Inverse proportion[/COLOR][/SIZE][/FONT][/B]

The relationship in which the value of one variable increases while the value of the second variable decreases at the same rate (in the same ratio).

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Inverter (NOT gate)[/COLOR][/SIZE][/FONT][/B]

A processing device within an electronic system, the NOT gate is a single input logic gate which 'inverts' its input. A logic 'HI' input will become a logic 'LOW' output and visa-versa. Here is the truth table:
A Z
0 1
1 0


[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Ion[/COLOR][/SIZE][/FONT][/B]

An electrically charged atom or molecule.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Ionization[/COLOR][/SIZE][/FONT][/B]

Process of forming ions from molecules.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Ionized[/COLOR][/SIZE][/FONT][/B]

An atom or a particle that has a net charge because it has gained or lost electrons.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Isostasy[/COLOR][/SIZE][/FONT][/B]

A balance or equilibrium between adjacent blocks of crust.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Isotope[/COLOR][/SIZE][/FONT][/B]

One of the possible varieties of atoms of a given element, having a certain number of neutrons.

[B][CENTER][FONT="Comic Sans MS"][SIZE="6"][COLOR="Blue"]J[/COLOR][/SIZE][/FONT][/CENTER][/B]


[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Joule [/COLOR][/SIZE][/FONT][/B]

Metric unit used to measure work and energy; can also be used to measure heat; equivalent to newton-meter.



[B][CENTER][FONT="Comic Sans MS"][SIZE="6"][COLOR="Blue"]K[/COLOR][/SIZE][/FONT][/CENTER][/B]


[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Kelvin[/COLOR][/SIZE][/FONT][/B]

The kelvin is the SI Unit of absolute temperature. 273.15 K is the same as 0 Celsius and 373.15 K is the same as 100 Celsius.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Kepler's first law[/COLOR][/SIZE][/FONT][/B]

Relationship in planetary motion that each planet moves in an elliptical orbit, with the sun located at one focus.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Kepler's laws of planetary motion[/COLOR][/SIZE][/FONT][/B]

The three laws describing the motion of the planets.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Kepler's second law[/COLOR][/SIZE][/FONT][/B]

Relationship in planetary motion that an imaginary line between the sun and a planet moves over equal areas of the ellipse during equal time intervals.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Kepler's third law[/COLOR][/SIZE][/FONT][/B]

Relationship in planetary motion that the square of the period of an orbit is directly proportional to the cube of the radius of the major axis of the orbit.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Kilo calorie[/COLOR][/SIZE][/FONT][/B]

The amount of energy required to increase the temperature of one kilogram of water one degree Celsius: equivalent to 1,000 calories.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Kilogram[/COLOR][/SIZE][/FONT][/B]

The kilogram is the SI unit of mass. It is defined as the mass of a particular cylinder of platinum.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Kinetic Energy[/COLOR][/SIZE][/FONT][/B]

Energy possessed by a body by the virtue of its motion is called kinetic energy. Kinetic energy = 1/2 m v².

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Kinetic friction[/COLOR][/SIZE][/FONT][/B]

A friction force between surfaces that are slipping past each other.

[B][CENTER][FONT="Comic Sans MS"][SIZE="6"][COLOR="Blue"]L[/COLOR][/SIZE][/FONT][/CENTER][/B]


[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Lamp[/COLOR][/SIZE][/FONT][/B]

A device intended to produce light energy. Modern lamps convert electrical energy to light energy via one of two main mechanisms - the filament lamp or the gas discharge lamp.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Laser[/COLOR][/SIZE][/FONT][/B]

The word laser was originally an abbreviation for Light Amplification by the Stimulated Emission of Radiation. Lasers have countless applications, many in medicine and communications. Lasers produce light which is monochromatic, coherent and tightly focussed. Lasers are used in the technique of photocoagulation (used to treat retinae).

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Latent heat of vaporization [/COLOR][/SIZE][/FONT][/B]

The heat absorbed when one gram of a substance changes from the liquid phase to the gaseous phase, or the heat released when one gram of gas changes from the gaseous phase to the liquid phase.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Latent heat of fusion[/COLOR][/SIZE][/FONT][/B]

The quantity of heat required to convert one unit mass of a substance from solid to the liquid state at its melting point (without any change in its temperature) is called its latent heat of fusion (L). The SI unit of latent heat of fusion is J kg-1.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Latent heat[/COLOR][/SIZE][/FONT][/B]

Latent heat, or hidden heat, is heat that is taken up and stored when a substance changes state from a solid to a liquid, from a liquid to a gas, or from a solid directly to a gas. It cannot be measured by a thermometer.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Law of Conservation of Energy[/COLOR][/SIZE][/FONT][/B]

The law of conservation of energy states that energy may neither be created nor destroyed. Therefore the sum of all the energies in the system is a constant.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Law of conservation of mass [/COLOR][/SIZE][/FONT][/B]

Same as law of conservation of matter; mass, including single atoms, is neither created nor destroyed in a chemical reaction.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Law of conservation of matter [/COLOR][/SIZE][/FONT][/B]

Matter is neither created nor destroyed in a chemical reaction.


[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Law of conservation of momentum [/COLOR][/SIZE][/FONT][/B]

The total momentum of a group of interacting objects remains constant in the absence of external forces.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Light [/COLOR][/SIZE][/FONT][/B]

Anything that can travel from one place to another through empty space and can influence matter, but is not affected by gravity.


[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Light Dependent Resistor (LDR)[/COLOR][/SIZE][/FONT][/B]

LDRs are designed so that their resistance depends on the intensity(brightness) of light falling on them.

[IMG]http://www.doctronics.co.uk/images/vdiv1.gif[/IMG]



[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Light Emitting Diode [/COLOR][/SIZE][/FONT][/B]

LEDs are simply diodes which emit light when connected correctly to a power supply.

[IMG]http://www.physics.utoledo.edu/~lsa/_color/33_led-diagram.jpg[/IMG]


[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Light-year [/COLOR][/SIZE][/FONT][/B]

The light-year (ly) is a unit of distance which is useful in astronomy. It is the distance which light (or any other form of electromagnetic radiation) travels in one year,approximately 9.5 x 10^11 km.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Line spectrum[/COLOR][/SIZE][/FONT][/B]

Narrow lines of color in an otherwise dark spectrum.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Lines of force[/COLOR][/SIZE][/FONT][/B]

Lines drawn to make an electric field strength map, with each line originating on a positive charge and ending on a negative charge; each line represents a path on which a charge would experience a constant force and lines closer together means a stronger electric field.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Liquids [/COLOR][/SIZE][/FONT][/B]

A phase of matter composed of molecules that have interactions stronger than those found in a gas but not strong enough to keep the molecules near the equilibrium positions of a solid, resulting in the characteristic definite volume but indefinite shape of a liquid.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Liquid Crystal Display (LCD)[/COLOR][/SIZE][/FONT][/B]

This is an output device. They run on almost no power since they don't produce their own light, but work by reflecting room or daylight.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Liter[/COLOR][/SIZE][/FONT][/B]

A metric system unit of volume, usually used for liquids.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Logic Diagram [/COLOR][/SIZE][/FONT][/B]

A simplified diagram of an electronic system, using rectangles to represent input and output devices along with the usual logic gate symbols for the AND, OR and NOT gate etc.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Logic Gate[/COLOR][/SIZE][/FONT][/B]

Logic gates allow an electronic system to make decisions based on a number of inputs. For example an OR gate can be used to illuminate a warning light if engine temperature is too high or if it is over-revved.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Logic State [/COLOR][/SIZE][/FONT][/B]

In a digital system, there are two logical states. One state is 'ON', 'HI' or 'logic 1' (all mean the same). The other is 'OFF', 'LOW', 'logic 0' (again all mean the same).

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Longitudinal waves[/COLOR][/SIZE][/FONT][/B]

The wave in which the particles of the medium oscillate along the direction of propagation of wave is called the longitudinal wave. Sound waves are longitudinal waves.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Long-sighted[/COLOR][/SIZE][/FONT][/B]

A problem with the accommodation ability of an eye. Basically, the eye can focus on far away objects with no problem, but can't properly focus on nearby objects. There can be two causes of this. The first occurs in older people, where the aging eye lens becomes less flexible and so cannot adopt the highly curved shape needed to focus at short range. This condition is called presbyopia. The second cause is that retina is too near to the lens - so that the focal point falls behind the retina. This is called hypermetropia or hyperopia. Long-sightedness can be treated by wearing spectacles which are convex in shape and therefore help to focus the image properly by reducing the overall focal length of the glasses and eye.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Lorentz transformation[/COLOR][/SIZE][/FONT][/B]

The transformation between frames in relative motion.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Loudness[/COLOR][/SIZE][/FONT][/B]

A subjective interpretation of a sound that is related to the energy of the vibrating source, related to the condition of the transmitting medium, and related to the distance involved.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Lubricant[/COLOR][/SIZE][/FONT][/B]

A lubricant is a substance which reduces friction between two surfaces. Examples are oil, water, air, bananas, seaweed.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Luminosity[/COLOR][/SIZE][/FONT][/B]

The total amount of energy radiated into space each second from the surface of a star.

[B][FONT="Comic Sans MS"][SIZE="4"][COLOR="Blue"]Luminous[/COLOR][/SIZE][/FONT][/B]

An object or objects that produce visible light; for example, the sun, stars, light bulbs, and burning materials are all luminous.