Page 38 - 12-phy-15 ELECTROMAGNETIC INDUCTION

15. Electromagnetic Induction eLearn.Punjab

15.7 The Fig.Q. 15.7 shows a coil of wire in the
xy plane with a magnetic field directed along

the y-axis.
Around which of the three coordinate

axes should the coil be rotated in order to
generate an emf and a current in the coil?

15.8 How would you position a flat loop of wire
in a changing magnetic field so that there is

no emf induced in the loop?

Fig. Q.15.7

15.9 In a certain region the earth’s magnetic field points vertically down. When a plane flies
due north, which wingtip is positively charged?

15.10 Show that e and Df/ Dt have the same units.

15.11 When an electric motor, such as an electric drill, is being used, does it also act as a

generator? If so what is the consequence of this?

15.12 Can a D.C motor be turned into a D.C generator? What changes are required to be done?

15.13 Is it possible to change both the area of the loop and the magnetic field passing through

the loop and still not have an induced emf in the loop?

15.14 Can an electric motor be used to drive an electric generator with the output from the

generator being used to operate the motor?

15.15 A suspended magnet is oscillating freely in a horizontal plane. The oscillations are

strongly damped when a metal plate is placed under the magnet. Explain why does this
occur?
15.16 Four unmarked wires emerge from a transformer. What steps would you take to

determine the turns ratio?

15.17 a) Can a step-up transformer increase the power level?

b) In a transformer, there is no transfer of charge from the primary to the secondary.
How is, then the power transferred?

15.18 When the primary of a transformer is connected to a.c mains the current in it

a) is very small if the secondary circuit is open, but
b) increases when the secondary circuit is closed. Explain these facts.

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