A ray of light travelling through a rarer medium is incident at very small angle ' $i$ ' on a glass slab and after refraction its velocity is reduced by $25 \%$. The angle of deviation is

Kinetic energy of a proton is equal to energy $E$ of a photon. Let ' $\lambda_1$ ' be the de-Broglie wavelength of proton and ' $\lambda_2$ ' be the wavelength of photon. If $\left(\frac{\lambda_1}{\lambda_2}\right) \propto E^n$ then the value of ' $n$ ' is

An inductance of 2 mH , a condenser of $20 \mu \mathrm{~F}$ and a resistance of $50 \Omega$ are connected in series to an a.c. source. The reactance of inductor and condenser are same. The reactance of either of them will be

Two sound waves having frequencies 250 Hz and 256 Hz superimpose to produce beat wave. The resultant beat wave has intensity maximum at $\mathrm{t}=0$. After how much time an intensity will be minimum produced at the same point?