Page 204 - NCERT Science Class 10 English Medium

Variable
n Connect the copper wire vertically between the resistance
points X and Y, as shown in Fig. 12.6 (a), in
series with the battery, a plug and key.
n Sprinkle some iron filings uniformly on the
cardboard. (You may use a salt sprinkler for this
purpose.)
n Keep the variable of the rheostat at a fixed
position and note the current through the
ammeter.
n Close the key so that a current flows through
the wire. Ensure that the copper wire placed
between the points X and Y remains vertically
straight. (a)
n Gently tap the cardboard a few times. Observe
the pattern of the iron filings. You would find
that the iron filings align themselves showing
a pattern of concentric circles around the
copper wire (Fig. 12.6).
n What do these concentric circles represent?
They represent the magnetic field lines.
n How can the direction of the magnetic field be
found? Place a compass at a point (say P) over
a circle. Observe the direction of the needle. The
direction of the north pole of the compass (b)
needle would give the direction of the field lines
Figure 12.6
Figure 12.6
Figure 12.612.6
Figure 12.6
Figure
produced by the electric current through the
(a) A pattern of concentric circles indicating
straight wire at point P. Show the direction by the field lines of a magnetic field around a
an arrow. straight conducting wire. The arrows in the
n Does the direction of magnetic field lines get circles show the direction of the field lines.
reversed if the direction of current through the (b) A close up of the pattern obtained.
straight copper wire is reversed? Check it.
What happens to the deflection of the compass needle placed at a
given point if the current in the copper wire is changed? To see this, vary
the current in the wire. We find that the deflection in the needle also
changes. In fact, if the current is increased, the deflection also increases.
It indicates that the magnitude of the magnetic field produced at a given
point increases as the current through the wire increases.
What happens to the deflection of the needle if the compass is moved
away from the copper wire but the current through the wire remains the
same? To see this, now place the compass at a farther point from the
conducting wire (say at point Q). What change do you observe? We see
that the deflection in the needle decreases. Thus the magnetic field
produced by a given current in the conductor decreases as the distance
from it increases. From Fig. 12.6, it can be noticed that the concentric
circles representing the magnetic field around a current-carrying straight
wire become larger and larger as we move away from it.

12.2.2 Right-Hand Thumb Rule

A convenient way of finding the direction of magnetic field associated
with a current-carrying conductor is given in Fig. 12.7.

Magnetic Effects of Electric Current 199

2024-25