With the help of a neat diagram describe a nuclear reactor.

ANS:



* A nuclear reactor is used for generation of electric power, production of fissile materials, nuclear research and for the production of man-made radioactive isotopes.

* As shown in figure a nuclear reactor consists of a core of reaction vessel called pressure chamber that can withstand very high pressures.

* The core consists of fuel rods (uranium rods) used as the fuel as well as a moderator like heavy water or graphite.

* The water is pumped into the pressure chamber to remove the heat generated during fission. This heat converts water into steam.

* This steam with high pressure and temperature is used to rotate the turbines of the generator and electric power is generated.

* The steam loses its heat in the process and cools down. It is allowed to cool further and the water thus obtained is reused in the process.

* The different fractions (products) obtained are : petroleum gases, petrol(gasoline), kerosene, diesel, lubricating oil, petroleum wax, tar, etc.

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# Explain : Nuclear Fusion.

ANS:


* The process in which two nuclei combine to form a heavy nucleus is called Nuclear Fusion.

* For example, two nuclei of heavy hydrogen (deuterium), 1H2 fuse to form one nucleus of helium, 2He3.

* During nuclear fusion, the mass of the products formed is slightly less than the mass of the reactants. This is called 'Mass Defect' and the 'missing mass' is converted into energy according to the Einstein's mass-energy equation, E = mc2.

* When two deuterium nuclei combine, following two reactions are possible:

1H2 + 1H2 → 2He3 + 0H1 + 3.3 MeV

1H2 + 1H2 → 1H3 + 1H1 + 4.0 MeV


* The main advantage of the above reaction is that we obtain about 33 g of deuterium from 1 cubic meter (1000 lit) of seawater. Thus, seawater contains about 1015 tons of deuterium.

* 1 gallon of deuterium releases energy equivalent to that released by 600 gallons of petrol.

* The following reaction involving tritium is possible at low temperature and it gives more energy.

1H3 + 1H2 → 2He4 + 0n1 + 17.6 MeV


* The proportion of tritium in seawater is less but we can obtain it by bombarding lithium isotope with a neutron.

3Li6 + 0n1 → 1H3 + 2He4

3Li7 + 0n1 → 1H3 + 2He4 + 0n1


* In thermonuclear fusion process, a fusion fuel is heated to 106 K when ionization takes place to form plasma.

* Plasma is a mixture of moving charged particles with equal number of negative and positive charges.

* It is difficult to control thermonuclear fusion. However, attempta are going on to develop a process of controlled fusion to obtain energy.

* Uncontrolled nuclear fusion is used to prepare weapons of mass destruction like hydrogen bomb.

* As compared to nuclear fission, the nuclear fusion has following advantages:

1. Fuel for nuclear fusion is cheap and easily available.

2. There is no requirement of disposing off of nuclear wastes.

3. It is pollution free.

# Write a note on Nuclear Hazards.

ANS:


* A nuclear blast can cause death of millions of people in a few seconds.

* It can damage huge structures like buildings.

* Heat produced during such blast can spread into large area destroying life.

* There are mainly two types of dangers from nuclear radiation : (1) Pathological danger (2) Genetic danger.

* Pathological effects cause diseases like cancer which may prove fatal.

* Genetic effects cause damage to the children of next generation in the form of various physical disabilities.

* Leakage of radiation from nuclear reactors adversely affect all spheres of the environment.

* The accidental leakage from a nuclear reactor in Chernobyl (Ukraine) in 1986 was so serious that about 50 tons of radioactive material had spread over a large area that thousands had died and about 2 lakh people had to be shifted to safer place. The radiation in this explosion was 200 times the radiation spread by the atomic bomb in Hiroshima and Nagasaki.

* The disposal of nuclear wastes, rods of nuclear fuel is a great problem as it spreads radiation continuously. Such material is at present buried very deep in the earth where it is unlikely to come in contact of underground water.

#


# distinguish between nuclear fission and nuclear fusion.

Ans:

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# Write a few points on Milky Way.

ANS:


* The galaxy in which our solar system is situated is called the Milky Way. Milky Way appears as a milky belt stretching from North to South during dark night when the sky is clear.
* Milky Way is spiral in shape when viewed from the top. When viewed from the sides, it is seen bulging at the center and tapered towards the ends.
* The diameter of Milky Way is about 1 lakh (0.1 million) light years and the thickness of the middle (bulging) part is about 15000-20000 light years.
* Sun (and therefore the solar system)is located at about 30000 light years away from the galactic center.
* The sun completes one revolution around the galactic center in 22.5 crore (225 million) years at the speed of 250 km/s.

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# Describe the use of artificial satellites in communication.

ANS:Following are the uses of artificial satellites in communication :


* For telecommunication(telephone).
* For television transmissions.
* For radio networks.
* For computer networks(internet).
* For countrywide classrooms.
* For teleconferencing.

# Explain the installation of artificial satellite by space shuttle.

ANS:


* A space shuttle carries a satellite to be launched in space with other instruments as payload.
* After the space shuttle has attained its required height in space, it continues to revolve around the earth in an orbit.
* Once it stabilizes properly in its orbit, a robotic arm in its upper part opens up.
* It holds the satellite to be installed and releases it in the space in its orbit.
* After the launching of satellite is over, the shuttle starts its return journey.

1. Write an explanatory note on Solar System with a diagram.

ANS:


* Our solar system consists of the Sun, nine planets revolving around it, 91 satellites revolving around the planets, more than 1 lakh asteroids, comets, etc.
* It is believed that the universe was formed due to Big Bang. After the big bang the sun was surrounded by a cloud of gases. These clouds were slowly converted into rocks due to contraction. These rocks kept on colliding with one another and during this process they either got broken or fused together to form bigger structures which we call planets. Thus, the present solar system came into existence.
* The gravitational force of sun provides the centripetal force required to keep the planets in their orbits.
* About 99% mass of the solar system comes is contained in sun. Sun is the main source of energy for planets. The amount of energy of sun reaching the earth is in desired proportion, essential for the origin and sustenance of life on earth.

Write a note on Sun.

ANS:


* Sun is the center of our solar system.
* About 99% of the mass of the solar system is contained in Sun. It mainly consists of hydrogen and helium along with elements like carbon, oxygen, magnesium, nickel, cobalt, etc.
* It is the main source of energy for earth and other planets.
* It is a sphere of hot gases with surface temperature of about 6000 K.
* The 400 km thick, bright layer around the sun is known as 'photosphere'.
* The layer beyond photosphere is invisible normally because the gases are very hot and less dense. But during solar eclipse, it becomes visible like a "crown". This layer is known as 'Corona'.



* The temperature in the core region is about 1.5 crore (15 million) K. At this temperature, thermonuclear fusion process takes place in which four hydrogen nuclei fuse to form a nucleus of helium.
* During this process some mass is lost which is converted into energy as per Einstein's mass-energy equation E = Δmc2, where Δm is the lost mass and c is the speed of light in vacuum.
* The mass of sun is 1.99 x 1030 kg. This mass is called 'Solar Mass' (M0).

# Write a note on Mercury.

ANS:


* It is the smallest planet of our solar system.
* It is nearest to the sun, i.e. its orbit is the smallest.
* Its mass is about (1/18)th the mass of the earth.
* Its gravitational field is weak.
* Its atmosphere is thin and consists mainly of vapours of sodium and potassium.
* Its day temperature is 427°C and the night temperature is (-173)°C.
* Its surface has many craters formed by meteors. Some of the craters are volcanoes.
* It has no satellite.
* Life is not possible on this planet.