Take a thin wooden plank covered with white paper
and make two holes on its surface as shown in figure
5(a). Pass insulated copper wire (24 gauge) through
the holes and wind the wire 4 to 5 times through holes
such that it looks like a coil (figure 5(a)). The ends of
the wire are connected to terminals of the battery
through a switch. Now switch on the circuit. Place a
compass needle on the plank at the centre of the coil. Put dots on either
side of the compass. Again place compass at one of the dots, put other dot
further. Do the same till you reach the edge of the plank. Now repeat this
for the other side of the coil from the centre. Then draw a line joining the
dots, you will get a field line of the circular coil. Do the same for the
other points taken in between the holes. Draw corresponding lines. You
will get field lines of the circular coil.
• Can you tell the direction of the magnetic field of the coil?
This could be answered from the orientation of the compass needle.
You can observe this when the compass needle is kept at the centre of the
coil. The direction in which the compass needle comes to rest indicates
the direction of the field due to the coil. Thus the direction of the field is
perpendicular to the plane of the coil.
• Why does the compass needle point in the direction of field?
Place the compass in front of one of the faces of the coil and observe
the orientation of the compass needle. Note the pole of the needle that
faces the coil. We know that south pole is attracted to the north pole. The
needle is oriented in such a way that its south pole
points towards the north pole of the coil. So we can
say that the direction of magnetic field, due to coil,
points towards you when the current in the coil is in
anticlockwise direction. Verify this in your experiment
(do not touch the wires of the coil). When the current
in the coil is in clock-wise direction, the direction of
magnetic field due to the coil points away from you. The direction of the
field due to coil or solenoid is determined by using right hand rule, which
states that,
“When you curl your right hand fingers in the direction of current,
thumb gives the direction of magnetic field.”
Observe the direction of magnetic field in figure 5(b)
Take a thin wooden plank covered with white paper
and make two holes on its surface as shown in figure
5(a). Pass insulated copper wire (24 gauge) through
the holes and wind the wire 4 to 5 times through holes
such that it looks like a coil (figure 5(a)). The ends of
the wire are connected to terminals of the battery
through a switch. Now switch on the circuit. Place a
compass needle on the plank at the centre of the coil. Put dots on either
side of the compass. Again place compass at one of the dots, put other dot
further. Do the same till you reach the edge of the plank. Now repeat this
for the other side of the coil from the centre. Then draw a line joining the
dots, you will get a field line of the circular coil. Do the same for the
other points taken in between the holes. Draw corresponding lines. You
will get field lines of the circular coil.