Energy released in the fission of a single uranium nucleus is 200 MeV . Then the number of fissions per second to produce 5 mW power is

The ratio of longest wavelengths of the spectral lines in the Lyman and Balmer series of hydrogen spectrum is

Half-life of a radioactive substance $A$ is two times the half-life of another radioactive substance $B$. Initially the number of nuclei of $A$ and $B$ are $N_A$ and $N_B$ respectively. After three half-lives of $A$, the number of nuclei of both are equal. Then $N_A / N_B$ is

The ratio of the relative strengths of strong and weak nuclear forces is