O
Objective Lens
In a refracting telescope the objective lens is the large lens which collects the dim light from objects in the night sky. The purpose of the objective is to collect as much light as possible. It does not magnify the image. With a larger objective, the image will be brighter and fainter objects will become visible.
Oblique
Describes a force that acts at some other angle, one that is not a direct repulsion or attraction.
Optical Fibres
Optically-pure glass fibre through which light can be reflected to transmit images or data from one end to the other.
Open Circuit
This is one of two types of circuit fault (the other being a short circuit). In an open circuit fault, there is a break in the circuit. This break will prevent any current from flowing. Open circuit faults register on an ohmmeter with an extremely high resistance.
Ohm (W)
The ohm is the SI unit of resistance. The resistance of an electrical component is one ohm (1 W) if, when a voltage of 1 V applied across it causes a current of 1 A to flow through it.
Ohm's Law
Georg S. Ohm discovered that for a conductor at constant temperature, the current which flows through the conductor is proportional to the voltage across it. The constant of proportionality is called the resistance of the conductor. The law is usually written as:
V = I R
Ohmic
Describes a substance in which the flow of current between two points is proportional to the voltage difference between them.
OR Gate
An OR 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.
Operational definition
A definition that states what operations should be carried out to measure the thing being defined.
Orbital
The region of space around the nucleus of an atom where an electron is likely to be found.
Origin
The only point on a graph where both the x and y variables have a value of zero at the same time.
Oscilloscope
Electronic instrument for viewing and measuring electrical and electronic signals.
Oscillatory motion
The to and fro motion of a body about its mean position is called oscillatory motion. Oscillatory motion is also called vibratory motion. Oscillatory motion is periodic in nature.