Take a thermocole sheet and fix two thin wooden sticks of height 1cm
which have small slit at the top of their ends. Arrange a copper wire of 24
gauge so that it passes through these slits and make a circuit. The circuit
consists of a 3 (or 9) volt battery, key and copper wire which are connected
in series as shown in figure 1. Now, keep a magnetic compass below the
wire. Bring a bar magnet close to the compass.
• Does the needle get deflected by the bar magnet?
• Why does the needle get deflected by the
magnet?
Take the bar magnet far away from the circuit
and switch on the circuit. Look for changes in
the position of the needle.
• What do you notice?
• Is there any change in the position of the compass needle?
• Which force is responsible for the deflection of the compass needle?
• Does the current-carrying wire apply a force on the needle?
• What do we call this force? (Recall the idea of field forces in class 8,
chapter “Force”).
In order to understand the reasons for the deflection of the compass
needle with no bar magnet near it we need to understand the idea of
‘magnetic field’ and the influence of electric field on magnetic field.