1. (d) The field consists of concentric circles centred on the wire.
2. (c) producing induced current in a coil due to relative motion between a magnet and
3. (a) generator
4. (d) A.C. generator has slip rings while the D.C. generator has commutator.
5. (c) increase heavily
6. (a) False
7. Three methods of producing magnetic fields are as follows:
(a) Magnetic field can be produced by placing a permanent magnet or a horse-shoe
magnet at the place, where magnetic field is required.
(b) Magnetic field is produced around a current carrying straight conductor or a
current carrying coil.
(c) A very good method to produce magnetic field is due to flow of current in a
8. When current is passed through a solenoid coil, magnetic field is produced due to
presence of turns in same direction. As a result, the resultant magnetic field is very
strong and uniform. Solenoid behaves like a strong bar magnet.
We can determine the poles of magnet formed by solenoid. The end of solenoid
connectd with positive terminal behaves like South Pole and the end connected with
negative terminal behaves as North Pole.
9. The force experienced by a current carrying conductor placed in a magnetic field is
largest when the conductor is placed with its length in a direction perpendicular to
that of magnetic field.
10. An electron beam moving horizontally from back wall towards the front wall is
equivalent to a current flowing in the opposite direction. The deflection of electron
beam as seen by the observer is to his right side. On applying Fleming’s left-hand
rule we find that the magnetic field is acting in vertically downward direction.
Electric motor labelled diagram of an electric motor is as follows:
Principle: A current-carrying conductor, when placed in a magnetic field,
experiences a force. If the direction of magnetic field and that of current are mutually
perpendicular then force acting on the conductor will be perpendicular to both and
will be the given by Fleming’s left-hand rule. Due to this force the conductor begins
to move, if it is free to rotate.
Working: Let the current in the coil ABCD of motor enters from the source battery
through the conducting brush X, flow along ABCD and finally flows back to the
battery through brush Y. On applying Fleming’s left-hand rule we find that force
acting on arm AB due to magnetic field pushes it downwards. But the force acting on
arm CD pushes it upwards. Thus, the coil and the axle rotate anticlockwise. Due to
action of split rings P and Q change their contacts with brushes. Now, P makes
contact with Y and Q with X. As a result, Current begins to flow in coil along DCBA.
The arms are pushed in opposite direction and coil continues to rotate in same
12. Electric motors are used in all devices where we want to convert electrical energy
into mechanical energy. In our houses, electric motors, coolers, mixer grinders,
washing machines, computers etc motor is used.
13. (i) When a bar magnet is pushed into the coil of insulated copper wire connected to a
galvanometer, galvanometer gives a deflection towards left.
(ii) When the bar magnet is withdrawn from inside the coil, again an induced current
is set in coil that deflect the galvanometer towards right.
(iii) If the bar magnet is held stationary inside the coil, then no induced current is set
and galvanometer does not show any deflection.
14. Yes, a current is induced in the coil B.
When the current in the coil A is changed, the magnetic field associated with it also
changes. As coil B is placed close to A, hence magnetic field lines around this coil also
change. Due to change in magnetic field lines associated with coil B, an induced
current is also induced in it.
15. (i) To know the direction of magnetic field produced around a straight conductor we
make use “Right hand thumb Rule”.
(ii) To find the direction of force experienced by a current carrying straight
conductor placed in a magnetic field we make use “Fleming’s left hand rule”.
(iii) For finding the direction of current induced in a coil we use “Fleming’s right
Electric generator labelled diagram is as follows:
Principle: An electric generator works on
the principle of electromagnetic
Working: Let the in the beginnings
brushes B1 and B2 are kept pressed
separately on rings R1 and R2
respectively. Let the axle attached to the
rings is rotated such that arm AB of the
coil moves up and arm CD moves down in the magnetic field. Due to rotation of arms
AB and CD induced current are set up in them. As per Fleming’s right hand rule,
induced current in these arms along the directions AB and CD respectively and
current flows into B1and B2.
After half rotation, arm AB moves downward and arms CD upward to change the
direction opposite to first case. Thus, after every half rotation current changes its
direction and an alternate current is obtained in the generator.
Brushes are kept pressed on the two slip rings separately. Outer ends of the brushes
are connected to the galvanometer. Thus, brushes help in transferring current from
the coil ABCD to external circuit.
17. If either the insulation of wires used in an electric circuit is damaged or there is a
fault in the appliances, live wire and neutral wire may come in direct contact. As a
result, the current in the circuit abruptly rises and short circuiting occurs.
18. The earth wires functions as a safety measure, especially for those appliances that
have a metallic body, like heater, electric, press, room cooler etc.
The metallic body of the appliance is connected to the earth wire, which provides a
low resistance conducting path for electric current. It ensures that any leakage of
current to the metallic body of an appliance keeps it potential same as of earth. As a
result, the user would not get severe electric shock, even if he touches the body of