Question

Activity
Take two different coils of copper wire having
large number of turns (say 50 and 100 turns
respectively). Insert them over a non-conducting
cylindrical roll, as shown in Fig. 13.17. (You may
use a thick paper roll for this purpose.)
Connect the coil-1. having larger number of
turns, in series with a battery and a plug key.
Also connect the other coil-2 with
galvanometer as shown.
Plug in the key. Observe the galvanometer. Is
there a deflection in its needle? You will observe
that the needle of the galvanometer instantly
jumps to one side and just as quickly returns to
zero. Indicating a momentary current in coll-2.
Disconnect coil-1 from the battery. You will
observe that the needle momentarily moves, but
to the opposite side. It means that now the
current flows in the opposite direction in coil-2.
HHHO)
Figure 13.17
Current is induced in coil-2 inhen current
in coll-1 is changed​

Answer 1

ANSWER

Choose the incorrect statement from the following regarding magnetic lines of field

(a) The direction of magnetic field at a point is taken to be the direction in which the north pole of a

magnetic compass needle points

(b) Magnetic field lines are closed curves

(c) If magnetic field lines are parallel and equidistant, they represent zero field strength

(d) Relative strength of magnetic field is shown by the degree of closeness of the field lines

Soln:

Answer is (c) If magnetic field lines are parallel and equidistant, they represent zero field strength

Explanation:

Option c) is incorrect because parallel lines of magnetic field represent uniform magnetic field.

2. If the key in the arrangement (Figure 13.1) is taken out (the circuit is made open) and magnetic field

lines are drawn over the horizontal plane ABCD, the lines are

(a) concentric circles

(b) elliptical in shape

(c) straight lines parallel to each other

(d) concentric circles near the point O but of elliptical shapes as we go away from it

Soln:

Answer is (a) concentric circles

EXPLAINATION

When open magnetic field lines are drawn over the horizontal plane ABCD, , then the magnetic field lines will be

in the form of concentric circles with centre at the axis of the conductor. This is because there will be no flow of

current and therefore there will be no magnetic field due to the conductor. So, at point O. only Earth’s magnetic

field will be present so the magnetic field lines will be in the form of concentric circles.

3. A circular loop placed in a plane perpendicular to the plane of paper carries a current when the key is

ON. The current as seen from points A and B (in the plane of paper and on the axis of the coil) is anti

clockwise and clockwise respectively. The magnetic field lines point from B to A. The N-pole of the

resultant magnet is on the face close to

(a) A

(b) B

(c) A if the current is small, and B if the current is large

(d) B if the current is small and A if the current is large

Soln:

Answer is (a) A

Explanation:

Direction of Magnetic field will be from south to northpole. Point A is showing northpole because field lines are pointing from B to A