 # Electromagnetic Induction | Old is Gold | XII

#### Short Questions

1.      What is Lenz’s law?
2.      Mention two types of loss in a transformer.
3.      Show that Lenz’s law is an example of conservation of energy.
4.      Two closely would circular coils have the same number of turns, but one has twice the radius of the other. What is the ratio of self inductance’s of the two coils?
5.      Why can`t a transformer be used to change the value of d.c. voltage?
6.      What is eddy current? Write down its uses?
7.      What are different power losses in a transformer? What measures do you take to minimize these losses?
8.      Why can`t a transformer be used to step up or down the d.c. voltage?
9.      A transformer cannot be used in do circuits, why?
10.  State Faraday`s laws of electromagnetic induction.
11.  A sheet of copper is placed between the poles of an electromagnet with the magnetic field perpendicular to the sheet. When it is pulled out, a considerable force is required, and the force required increases with speed, why?
12.  Permanent magnets are made of steel while the core of transformer is made of soft iron. Why?
13.  A student asserted that if a permanent magnet is dropped down a vertical copper pipe, it eventually reaches a terminal velocity even if there is no air resistance. Why should this be?
14.  If a permanent magnet is dropped down a vertical copper pipe, it eventually reaches a terminal velocity even if there is no air resistance. Why should this be?
15.  Describe the theory and working of an a.c. generator.

#### Long Questions

1.      Obtain the expression for the emf induced in the conductor moving in a magnetic field.
2.      State the laws of electromagnetic induction. Derive an expression for the emf induced in a conductor moving in a magnetic field.
3.      Deduce an expression for induced emf in a coil rotating in a magnetic field.
4.      State Lenz`s law and explain how this law leads to the conservation of energy principle.
5.      State Faraday`s laws of electromagnetic induction. Deduce an expression for induced emf in a coil rotating in a magnetic field.
6.      State and explain Faraday`s law of electromagnetic induction. Derive an expression for the induction a coil rotating in a uniform magnetic field.
7.      State Faraday`s law of electromagnetic induction. Derive an expression for the induced in a straight conductor moving at right angle to the direction of a uniform magnetic field.
8.      A metallic rod is moving in a magnetic field. Determine the emf induced across it.