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

The graph given in the figure shows the variation of photo current $(I)$ and the applied voltage ( $V$ ) for two different materials and for two different intensities of the incident radiations. Then the curves which represent the same material are

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

When an $n$-type semiconductor is heated