I did a physics lab of magnetic force and induction. In one part we used an elec

Question

I did a physics lab of magnetic force and induction. In one part we used an electro magnet and inserted a small coil which was attached to a DC power supply into a large coil which was then connected to a galavanometer.

My question is:

A) why did the needle go to the right when the DC power supply was turned on?

B) Why did the needle go to the left when the DC power supply was turned off?

C) Why did the induced current go to zero when the voltage was held constant?

Please explain using Faradays and Lenz law and physics background info. Thank you. Will rate and comment best answer.

Explanation / Answer

According to Faraday's law, the current is induced in the outer coil when there is a change in the magnetic flux.
And according to the Lenz law, the current in induced in that direction so as to oppose the change in the magnetic flux.

a.) So, initially, when there was no power supply, the magnetic flux inside the smaller coil was zero. And when the DC power supply was turned on the magnetic flux increased from zero to some value. And since there was a change (increase) in magnetic flux at this instant, current is induced in the outer coil in that direction (apparently, right) so as to oppose this change and this induced current is what was detected by the galvanometer.

b.) Later, when there was a steady power supply, the magnetic flux inside the smaller coil was constant. And when the DC power supply was turned off, the magnetic flux decreased from that constant value to zero. And since there was a change (decrease) in magnetic flux at this instant, current is induced again in the outer coil in that direction (apparently, left which is opposite to the earlier direction) so as to oppose this change and this induced current is what was shown in the galvanometer. The needle this time moved to the left because the induced current this time was in the opposite direction.

c.) Please note that only change in the magnetic flux will induce a current and not the flux itself. So, when the voltage was held constant, the magnetic flux also remained constant and hence no change in the magnetic flux to generated the induced current.

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