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

The half lives of two radioactive material $A$ and $B$ are respectively $T$ and $2 T$. If the ratio of the initial masses of the materials $A$ and $B$ is $8: 1$. Then, the time after which the ratio of the masses of the materials $A$ and $B$ becomes $4: 1$ is

The energy released by the fission of one uranium nucleus is 200 MeV . The number of fissions per second required to produce 128 W power is