Physics Class 12 NCERT Solutions: Chapter 13 Nuclei Part 7 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Difference between Fusion and Fission

Q: 1. The fission properties of are very similar to those of .

The average energy released per fission is 180 MeV. How much energy, in , is released if all the atoms in 1 kg of pure undergo fission?


Average energy released per fission of ,

Amount of pure ,

Avogadro number

Mass number of

1 mole of contains atoms.

of contains contains

∴ Total energy released during the fission of of is calculated as:

Hence, is released if all the atoms in of pure undergo fission.

Q: 18. A fission reactor consumes half of its fuel in . How much did it contain initially? Assume that the reactor operates 80 % of the time, that all the energy generated arises from the fission of and that this nuclide is consumed only by the fission process.


Half- life of the fuel of the fission reactor, years

We know that in the fission of of nucleus, the energy released is equal to .


The total energy generated per gram of is calculated as:

The reactor operates only of the time.

Hence, the amount of consumed in 5 years by the fission reactor is calculated as:

∴ Initial amount of

Q: 19. How long can an electric lamp of be kept glowing by fusion of of deuterium? Take the fusion reaction as


The given fusion reaction is:

Amount of deuterium,

Of deuterium contains atoms.

of deuterium contains atoms

It can be inferred from the given reaction that when two atoms of deuterium fuse, energy is released.

∴ Total energy per nucleus released in the fusion reaction:

Power of the electric lamp,

Hence, the energy consumed by the lamp per second

The total time for which the electric lamp will glow is calculated as: