Professor G. S. Mehmi

Faraday gave two laws on electromagnetic induction. Faraday's Ist Law : This law states that whenever magnetic flux (magnetic lines of force) linked with any closed circuit (loop) changes, an induced e.m.f. and hence, induced current is produced in the circuit which lasts so long as the flux changes. The direction of induced curret is such that it is inverse when flux increases and direct when flux decreases. Faraday's 2nd Law : The magnitude of induced e.m.f. produced in a circuit (coil) directly proportional to the rate of is change of magnetic flux linked with the circuit. If flux d ∮ changes in time dt, then rate of change of magnetic flux becomes  d ∮/dt. According to Faraday's 2nd law,  E ∝   d ∮/dt    ...(1) Applying constant of proportionality, then equation (1) becomes, E = - 1 d ∮/dt   ...(2) where -1 is constant of proportionality and - ve sign is represent the opposing nature of induced e.m.f. and induced current. If coil has N tur...

The construction of a ruby laser is shown in fig1. It consists of a pink rod, which is a crystal of aluminum oxide doped with 50% chromium oxide and 4 cm in length. Its ends are optically flat and one is fully and other is partly silvered. A coiled flash tube (Xenon lamp) surrounds the rod. When flash of light takes place, green and yellow light is absorbed by chromium ions and thus they are excited to higher energy states while the red is allowed to pass through. This red light suffers successive reflections at the silvered ends. Excited atoms jump to a common metastable state giving energy to the crystal. Energy in metastable state is equal to the energy of red light which is already present. Thus, the ions return to the ground state with the stimulated emission of red radiations. Since large number of chromium atoms are present in metastable state, thus stimulated emission is continuously amplified and hence an intense coherent beam of light leaked out into air through partly silver...