The operation of a nuclear reactor is said to be critical when the value of neutron multiplication factor $K i s$

An $\alpha$-particle of energy $E$ is liberated during the decay of a nucleus of mass number 236. The total energy released in this process is

The related effort to derive the properties of a bigger, more complex system from the properties and interactions of its constituent simpler parts is

The ratio of the wavelengths of radiation emitted when an electron in the hydrogen atom jumps from 4th orbit to 2 nd orbit and from 3rd orbit to 2 nd orbit is