Page 205 - NCERT Science Class 10 English Medium

Imagine that you are holding a current-carrying straight
conductor in your right hand such that the thumb points towards
the direction of current. Then your fingers will wrap around the
conductor in the direction of the field lines of the magnetic field, as
shown in Fig. 12.7. This is known as the right-hand thumb rule*.

Example 12.1
Figure 12.7
Figure
Figure 12.712.7 A current through a horizontal power line flows in east to west
Figure
Figure 12.7
12.7
Right-hand thumb rule direction. What is the direction of magnetic field at a point directly
below it and at a point directly above it?
Solution
The current is in the east-west direction. Applying the right-hand
thumb rule, we get that the magnetic field (at any point below or
above the wire) turns clockwise in a plane perpendicular to the wire,
when viewed from the east end, and anti-clockwise, when viewed
from the west end.

Q U E S T I O N S

?
1. Draw magnetic field lines around a bar magnet.
2. List the properties of magnetic field lines.
3. Why don’t two magnetic field lines intersect each other?

12.2.3 Magnetic Field due to a Current through a
Circular Loop

We have so far observed the pattern of the magnetic field lines
produced around a current-carrying straight wire. Suppose
this straight wire is bent in the form of a circular loop and a
current is passed through it. How would the magnetic field
lines look like? We know that the magnetic field produced
by a current-carrying straight wire depends inversely on the
distance from it. Similarly at every point of a current-carrying
circular loop, the concentric circles representing the magnetic
field around it would become larger and larger as we move
away from the wire (Fig. 12.8). By the time we reach at the
centre of the circular loop, the arcs of these big circles would
Figure 12.812.8 appear as straight lines. Every point on the wire carrying
Figure 12.8
12.8
Figure 12.8
Figure
Figure
Magnetic field lines of the field current would give rise to the magnetic field appearing as
produced by a current-carrying straight lines at the center of the loop. By applying the right
circular loop
hand rule, it is easy to check that every section of the wire
contributes to the magnetic field lines in the same direction
within the loop.
* This rule is also called Maxwell’s corkscrew rule. If we consider ourselves driving a
corkscrew in the direction of the current, then the direction of the rotation of
corkscrew is the direction of the magnetic field.

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