Page 202 - NCERT Science Class 10 English Medium

n Mark the position of two ends of the needle.
n Now move the needle to a new position
such that its south pole occupies the
position previously occupied by its north
pole.
n In this way, proceed step by step till you
reach the south pole of the magnet as
shown in Fig. 12.3.
Figure 12.312.3
Figure
Figure 12.3
Figure 12.3
Figure 12.3
n Join the points marked on the paper by a
Drawing a magnetic field line with the help of a
smooth curve. This curve represents compass needle
a field line.
n Repeat the above procedure and draw as
many lines as you can. You will get a
pattern shown in Fig. 12.4. These lines
represent the magnetic field around the
magnet. These are known as magnetic
field lines.
n Observe the deflection in the compass
needle as you move it along a field line.
The deflection increases as the needle is
moved towards the poles.
Figure
Figure
Figure 12.412.4
Figure 12.4
Figure 12.4
12.4
Field lines around a bar magnet
Magnetic field is a quantity that has both direction and magnitude.
The direction of the magnetic field is taken to be the direction in which a
north pole of the compass needle moves inside it. Therefore it is taken
by convention that the field lines emerge from north pole and merge at
the south pole (note the arrows marked on the field lines in Fig. 12.4).
Inside the magnet, the direction of field lines is from its south pole to its
north pole. Thus the magnetic field lines are closed curves.
The relative strength of the magnetic field is shown by the degree of
closeness of the field lines. The field is stronger, that is, the force acting
on the pole of another magnet placed is greater where the field lines are
crowded (see Fig. 12.4).
No two field-lines are found to cross each other. If they did, it would
mean that at the point of intersection, the compass needle would point
towards two directions, which is not possible.

ARRYING
MAGNETIC FIELD DUE TO A CURRENT-CARRYING
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12.2 .2 .22 2 .2 MAMAGNETIC FIELD DUE TO A CURRENTGNETIC FIELD DUE TO A CURRENT-- -CCARRYING
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C CONDUCTORONDUCTOR
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In Activity 12.1, we have seen that an electric current through a
metallic conductor produces a magnetic field around it. In order to
find the direction of the field produced let us repeat the activity in the
following way –
Magnetic Effects of Electric Current 197
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