Exercise

Does an iron bar magnet retain its magnetism when melted? Give a reason for your answer.

What are the causes of displacement current?

Write two main observations of photoelectric effect experiment which could only be explained by Einstein's photoelectric equation.

Critical angle of a medium is $60°$.Find its refractive index.

Twelve resistors each of resistance $r$ are joined to form a cube as shown in the figure given below. Find the equivalent resistance between the diagonally opposite points $A$ and $F$.

 Describe any two characteristic features which distinguish between interference and diffraction phenomena. Derive the expression for the intensity at a point of the interference pattern in Young’s double slit experiment.

The nucleus ${}_{92}{}^{235}Y$, initially at rest, decays into ${}_{90}{}^{231}X$ by emitting an $\alpha -$ particle.

${}_{92}{}^{235}Y\to {}_{90}{}^{231}X+{}_2{}^4\mathrm{He}+$energy

The binding energy per nucleon of the parent nucleus, the daughter nucleus and $\alpha -$particles are $7.8 \mathrm{Mev}, 7.835 \mathrm{Mev}$ and $7.07 \mathrm{Mev}$, respectively. Assuming the daughter nucleus to be formed in the excited state and neglecting its share in the energy of the reaction, find the speed of the emitted $\alpha -$particle. (Mass of $\alpha -$particle$=6.68\times {10}^{-27} \mathrm{kg}$)

Derive an expression for the impudence of a series LCR circuit connected to an ac supply of variable frequency. Plot a graph showing variation of current with the frequency of the applied voltage. Explain briefly how the phenomenon of resonance in the circuit can be used in the tuning mechanism of a radio or a TV set.