Question

What is the change in the form of energy that is shown by the change in direction of the compass needle when an electric current is passed beneath it?

When the magnet is moved inside the coil of wire, what does the Galvinometer indicate?

Would making the fixed magnet stronger, have an effect on the amount of current produced?

Answer 1

A current carrying wire induces a magnetic field around it. So when a wire carrying an electric current is placed near a compass needle, it induces a magnetic field. And this magnetic field, in turn, exerts a force on the magnetic needle of the compass and forces it to align in the direction of the current carrying wire's magnetic field. The change in magnetic energy around the compass causes this change.

When a magnet is moved inside the coil, the galvanometer pointer moves to one side. When the magnet is taken out the pointer deflects in the opposite direction. This is because of Lenz's law. This law states that "the current induced in a circuit due to a change or a motion in a magnetic field is so directed as to oppose the change in flux and to exert a mechanical force opposing the motion." This means that the current induced in the circuit as a result of which there is a deflection in the galvanometer is an attempt to oppose the change in flux.

Making the fixed magnet stronger will not have an effect on the amount of current produced. This is because the current is produced when there is an induced emf. And emf is induced only when the flux changes. For the flux to change either the magnetic field, or area, or the orientation must keep changing. A constant magnetic field results in no flux change and as a result, there is no effect on the induced current.

Here, = Induced emf

N = Number of turns in coil

= Flux = B.A

where, B = magnetic field and A = area