12th physics. NCERT notes

Nuclear Energy

Energy then can be released if less tightly bound nuclei are transmuted into more tightly bound nuclei. Two such processes, which we have already referred to, are fission and fusion.
In conventional energy sources like coal or petroleum, energy is released through chemical reactions. The energies involved are of the order of electron volts per atom. As we have seen, energies involved in nuclear processes are million times larger (in MeVs per nucleon). This means that for the same quantity of matter, nuclear sources will give a million times the larger energy than conventional sources. One kilogram of coal on burning gives 107 J of energy, whereas 1 kg of uranium, which undergoes fission, will generate on fission 1014 J of energy.

Nuclear fusion and nuclear fission are different types of reactions that release energy due to the presence of high powered atomic bonds between particles found within a nucleus. In fission, an atom is split into two or more smaller, lighter atoms. Fusion, in contrast, occurs when two or smaller atoms fuse together, creating a larger, heavier atom.

Comparison Chart

Nuclear FissionNuclear Fusion
DefinitionFission is the splitting of a large atom into two or more smaller ones.Fusion is the fusing of two or more lighter atoms into a larger one.
Natural occurrence of the processFission reaction does not normally occur in nature.Fusion occurs in stars, such as the sun.
By products of the reactionFission produces many highly radioactive particles.Few radioactive particles are produced by fusion reaction, but if a fission “trigger” is used, radioactive particles will result from that.
ConditionsCritical mass of the substance and high-speed neutrons are required.High density, high temperature environment is required.
Energy requirementTakes little energy to split two atoms in a fission reaction.Extremely high energy is required to bring two or more protons close enough that nuclear forces overcome their electrostatic repulsion.
Energy ReleasedThe energy released by fission is a million times greater than that released in chemical reactions, but lower than the energy released by nuclear fusion.The energy released by fusion is three to four times greater than the energy released by fission.
Nuclear weaponOne class of nuclear weapon is a fission bomb, also known as an atomic bomb or atom bomb.One class of nuclear weapon is the hydrogen bomb, which uses a fission reaction to “trigger” a fusion reaction.
Energy ProductionFission is used in nuclear power plants.Fusion is an experimental technology for producing power.
FuelUranium is the primary fuel used in power plants.Hydrogen isotopes (Deuterium and Tritium) are the primary fuel used in experimental fusion power plants.


Nuclear Fission

It is the process in which a heavy nucleus splits up into two nuclei of nearly comparable masses.

Nuclear Fusion

It is the process in which two or more small nuclei fuse together to form a single heavy nucleus.

The mass of the single heavy nucleus formed is less than the total initial mass of the mass of the parent nuclei.

This difference in mass appears in the form of energy (as per, E = mc2).

Enormous amount of energy produced by the sun is due to the phenomenon of nuclear fusion.


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