Physics Class 12 NCERT Solutions: Chapter 13 Nuclei Part 7

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Difference between fusion and fission

Difference between Fusion and Fission

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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: