Page 206 - NCERT Science Class 10 English Medium

We know that the magnetic field produced by a current-carrying
wire at a given point depends directly on the current passing through it.
Therefore, if there is a circular coil having n turns, the field produced is
n times as large as that produced by a single turn. This is because the
current in each circular turn has the same direction, and the field due to
each turn then just adds up.

Activity 12.612.6
Activity 12.6
Activity 12.6
Activity 12.6
Activity
n Take a rectangular cardboard having two holes.
Insert a circular coil having large number of turns
through them, normal to the plane of the cardboard.
n Connect the ends of the coil in series with a battery,
a key and a rheostat, as shown in Fig. 12.9.
n Sprinkle iron filings uniformly on the cardboard.
n Plug the key.
n Tap the cardboard gently a few times. Note the
12.9
Figure
Figure 12.9
Figure 12.9
Figure
pattern of the iron filings that emerges on the Figure 12.912.9
Magnetic field produced by a current-
cardboard.
carrying circular coil.
12.2.4 Magnetic Field due to a Current in a Solenoid
A coil of many circular turns of insulated copper wire wrapped
closely in the shape of a cylinder is called a solenoid. The pattern
of the magnetic field lines around a current-carrying solenoid is
shown in Fig. 12.10. Compare the pattern of the field with the
magnetic field around a bar magnet (Fig. 12.4). Do they look
similar? Yes, they are similar. In fact, one end of the solenoid
behaves as a magnetic north pole, while the other behaves as the
Figure
south pole. The field lines inside the solenoid are in the form of Figure 12.1012.10
Figure
Figure 12.10
12.10
Figure 12.10
parallel straight lines. This indicates that the magnetic field is Field lines of the magnetic field
the same at all points inside the solenoid. That is, the field is through and around a current
carrying solenoid.
uniform inside the solenoid.
A strong magnetic field produced inside a solenoid can be
used to magnetise a piece of magnetic material, like soft iron,
when placed inside the coil (Fig. 12.11). The magnet so formed is
called an electromagnet.
Q U E S T I O N S
Figure
Figure 12.11
Figure
Figure 12.1112.11
Figure 12.11
12.11
A current-carrying solenoid coil
1. Consider a circular loop of wire lying in is used to magnetise steel rod
the plane of the table. Let the current inside it – an electromagnet.
pass through the loop clockwise. Apply
the right-hand rule to find out the
direction of the magnetic field inside ?
and outside the loop.
2. The magnetic field in a given region is
uniform. Draw a diagram to represent it.

Magnetic Effects of Electric Current 201

2024-25