The current passing through a coil of 120 turns and inductance 40 mH is 30 mA . The magnetic flux linked with the coil is

A resistor of resistance $R$, inductor of inductive reactance $2 R$ and a capacitor of capacitive reactance $X_C$ are connected in series to an AC source.If the series $L-C-R$ circuit is in resonance, then the power factor of the circuit and the value, $X_C$ are respectively

The rms value of the electric field of an electromagnetic wave emitted by a source is $660 \mathrm{NC}^{-1}$. The average energy density of the electromagnetic wave is

The maximum wavelength of light which causes photoelectric emission from photosensitive metal surface is $\lambda_0$. Two light beams of wavelengths $\frac{\lambda_0}{3}$ and $\frac{\lambda_0}{9}$ incident on the metal surface. The ratio of the maximum velocities of the emitted photoelectrons is