A metallic bob A oscillates through the space between the poles of an electromagnet . The oscillation are more quickly damped when the circuit is on, as compared to the case when the circuit is off. Explain.

The motion of copper plate is damped when it is allowed to oscillate between the two poles of a magnet what is the cause of this damping ?

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?

In an oscillating LC circuits the maximum charge on the capacitors is Q. The charge on the capacitor when the energy is stored equally between the electric and magnetic field is

A metal bob is suspended from a coiled spring. When set into vertical vibrations on the earth. It oscillates up and down with frequency f. If the same experiment is carried out in a satellite circling the Earth the frequency of vibration will be……………

A matel wire PQ of mass 10g lies at rest on two horizontal metal rails separated by 4.90 cm . A vertically downward magnetic field of magnitude 0.800 T exists in the space. The resistance of the circuit is slowly decreased and it is found that when the resistance goes below 20.0 Omega , the wire PQ starts sliding on the rails. Find the coefficient of friction.

It has been determined experimentally that when light falls on a metal surface, the surface emits electrons. For example, you can start a current in a circuit just by shining a light on a metal plate. a. What is your explanation? b. Mention some other methods in which electron emission is possible. c. Are stopping potential and cut off potential the same?

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?