EXERCISES
1. Which of the following correctly describes the magnetic field near a long
straight wire?
(a)The field consists of straight lines perpendicular to the wire.
(b)The field consists of straight lines parallel to the wire.
(c)The field conststs of radial lines originating from the wire.
(d)The field consists of concentric circles centred on the wire.
2. The phenomenon of electromagnetic induction is
(a)the process of charging a body.
(b) the process of generating magnetic field due to a current passing
through a coil.
(c) producing induced current in a coil due to relative motion between a
magnet and the coil.
(d)the process of rotating a coil of an electric motor.
3. The device used for producing electric current is called a
(a)generator
(b), galvanometer.
(c)ammeter,
(d)motor.
4. The essential difference between an AC generator and a DC generator is that
(a) AC generator has an electromagnet while a DC generator has
permanent magnet.
(b)DC generator will generate a higher voltage.
(c)AC generator uwill generate a higher voltage.
(d) AC generator has slip rings while the DC generator has a commutator
5. At the time of short circuit, the current in the circuit
(a)does not change.
(b)reduces substantially.
(c)increases heavily.
(d)vary continuously.
6. State whether the following statemnents are true or false.
(a)An electric motor converts mechanical energy into electrical energy.
(b)An electric generator works on the principle of electromagnetic induction.
(c)The field at the centre of a long circular coil carrying current will be
parallel straight lines.
(d)A wire with a green insulation is usually the live wire of an electric supply.
7. List three sources of magnetic fields.
8. How does a solenotd behave like a magnet? Can uou determine the north and
south poles of a current-carrying solenoid with the help of a bar magneť? Explatn.
9. When is the force experienced by a current-carrying conductor placed in a mugrtette
field largest?
10. Imagine that you are sitting in a chamber with your back to one wall. An electron
beam, moving horizontally from back wall towards the front wall, is deflected by a
strong magnetic field to your right side. What is the direction of magnetic field?
11. Draw a labelled diagram of an electric motor. Explain its principle and working.
What is the function of a split ring in an electric motor?
12. Name some devices in which electric motors are used.
13. A coil of insulated copper wire is connected to a galvanometer. What will happen if
a bar magnet is (i) pushed into the coil, (ii) withdrawn from inside the coil, (iii) held
stationary inside the coil?
14. Two circular coils A and B are placed closed to each other. If the current in the coil
A is changed, will some current be induced in the coil B? Give reason.
15. State the rule to determine the direction of a (i) magnetic field produced around a
straight conductor-carrying current, (ü) force experienced by a current-carrying
straight conductor placed in a magnetic field which is perpendicular to it, and
(ii) current induced in a coll due to its rotation in a magnetic field.
16. Explain the underlying principle and wworking of an electric generator by drawing
a labelled diagram. What is the function of brushes?
17. When does an electric short circuit occur?
18. What is the function of an earth wire? Why is it necessary to earth metallic
appliances?
