Let ‘θ’ be the angle between direction of current and magnetic field, then the force acting on the current carrying wire is given by

F = ILB sinθ (at any angle) ...................(5)

• How could you find its direction?

You can use right hand rule to find out the direction of force on the current carrying wire.

Let us see the result of force applied on a current carrying wire by an experiment

Take a wooden plank. Fix two long wooden sticks on it. These wooden sticks are split at their top ends.

A copper wire is passed through these splits and the ends of the wire are connected to battery of 3 volt, through a switch. Close the switch to make the circuit. Current passes through the wire. Now bring a horseshoe magnet near the copper wire as shown in figure 10.

• What happens to the wire?

• In which way does it deflect?

Use the right thumb rule to find the direction of force.

• Is the direction of deflection observed experimentally same as that of the theoretically expected one?

Change polarities of the horse shoe magnet. Again observe the deflection.

Repeat this by changing the direction of current in the circuit.

• Does the right hand rule give the explanation for the direction of magnetic force exerted by magnetic field on the wire?

Right hand rule helps you to find the direction of magnetic force exerted by the magnetic field on current carrying wire. It does not help you explain the reason for deflection of wire.

• Can you give a reason for it?

Imagine a situation where there is no current in the wire. Then there exists only magnetic field due to external source (horse shoe magnet). When there is a current in the wire, it also produces a magnetic field. These fields overlap and give non- uniform field. Let us see this clearly with diagrams.