One of the necessary condition for total internal reflection to take place is

( $$\mathrm{i}=$$ angle of incidence, $$\mathrm{i}_{\mathrm{c}}=$$ critical angle)

In the given circuit, if $$\frac{\mathrm{dI}}{\mathrm{dt}}=-1 \mathrm{~A} / \mathrm{s}$$ then the value of $$\left(V_A-V_B\right)$$ at this instance will be

An inductor of $$0.5 \mathrm{~mH}$$, a capacitor of $$20 ~\mu \mathrm{F}$$ and a resistance of $$20 \Omega$$ are connected in series with a $$220 \mathrm{~V}$$ a.c. source. If the current is in phase with the e.m.f. the maximum current in the circuit is $$\sqrt{x} A$$. The value of '$$x$$' is

The wavelength of radiation emitted is '$$\lambda_0$$' when an electron jumps from the second excited state to the first excited state of hydrogen atom. If the electron jumps from the third excited state to the second orbit of the hydrogen atom, the wavelength of the radiation emitted will be $$\frac{20}{x} \lambda_0$$. The value of $$x$$ is