When the magnetic flux associated with a coil changes an emf is induced in the circuit.
A. State Faraday's law of electromagnetic induction.
B. Mention the physical significance of Len'z law with an example.
C. When an electrical appliance is switched off, sparking occurs. Why?

Fig. E.I show s magnet coil experiment of electromagnetic induction. What happens when a. i. The number of turns of the coil is inceased. ii. The streangth of the magnet is increased. iii. The speed of motion of the magnet is increased. b. An induced e.m.f. has no direction of its own. Why?

Figure shows a metal rod PQ resting on the smooth rails AB and positioned between the poles of a permanent magnet. The rails, the rod and the magnetic field are in three mutually perpendicular directions. A galvonometer G connects the rails through a switch K. Length of rod = 15 cm, B = 0.50 T, resistance of the closed loop containing the rod = 9.0mOmega . Assume the field to be uniform. a. Suppose K is open and the rod is moved with a speed of 12cms^(-1) in the direction shown. Give the polarity and magnitude of the induced emf. b. Is there an excess charge built up at the ends of the rods when K is open? What if K is closed? c. With K open and the rod moving uniformly, there is no net force on the electrons in the rod PQ eventhough they do experience magnetic force due to the motion of the rod. Explain. d. What is the retarding force on the rod when K is closed? e. How much power is required (by an external agent) to keep the rod moving at the same speed (=12cms^(-1)) when K is closed? How much power is required when K is open? f. How much power is dissipated as heat in the closed circuit? What is the source of this power? g. What is the induced emf in the moving rod if the magnetic field is parallel to the rails instead of being perpendicular?

A rectangular metallic loop of length l and width b is placed coplanerly with a long wire carrying a current I . The loop is moved perpendicular to the wire with a speed v in the plane containing the wire and the loop. Calculate the emf induced in the loop when the rear end of hte loop is at a distance a from the wire. Solve by unsing Faraday's law for the flux thrugh the loop and also by replacing different sagments with equivalent batteries.

A metal block of heat capacity 90J//.^(@)C placed in a room at 25^(@)C is heated electrically. The heater is switched off when the temperature reaches 35^(@)C . The temperature of the block rises at the rate of 2^(@)C//s just after the heater is switched on and falls at the rate of 0.2^(@)C//s just after the heater is switched off. Assume Newton's law of cooling to hold (a) Find the power of the heater. (b) Find the power radiated by the block just after the heater is switched off. (c ) Find the power radiated by the block when the temperature of the block is 30^(@)C . (d) Assuming that the power radiated at 30^(@)C respresents the average value in the heating process, find the time for which the heater was kept on.