An AC circuit contains resistance of $12 \Omega$ and inductive reactance $5 \Omega$. The phase angle between current and potential difference will be

In an intrinsic semiconductor, at an ordinary temperature, the correct relation between the number of electrons per unit volume $n_e$ and number of holes per unit volume $n_h$.

By increasing the aperture of the objective lens, wavelength of light, focal length of the objective lens and the resolving power of an astronomical telescope respectively

Two galvanometers $A$ and $B$ require currents of 4 mA and 7 mA , respectively to produce the same deflection of 20 divisions. If $S_A$ and $S_B$ are their sensitivities respectively, then