The self inductance of an air-core inductor (solenoid) is $0.03$ mH. By introducing an iron core into inductor the self-inductance increases to $30$ mH. The relative permeability of the core used is

A coil of effective area $3$ m$^2$ is placed at right angles to a magnetic field of induction $0.05$ Wb/m$^2$. If the field is decreased to $20\%$ of its original value in $10$ second, the e.m.f. induced in the coil will be

In a series LCR circuit, the voltage across R is $100$ V, $R = 1\,\text{K}\,\Omega$ and $C = 2\,\mu\text{F}$. The angular frequency $\omega$ is $200$ rad s$^{-1}$. At resonance, the voltage across '$L$' is

Which graph shows the correct variation of r.m.s. current '$i$' with frequency '$f$' of a.c. in case of series resonant circuit ?