[Physics] Moving Coil Galvanometer

electricityelectromagnetic-inductionelectromagnetism

Considering a moving coil galvanometer that isn't connected in a circuit, say I deflect it and release it. The coil should start oscillating. But now, what if I suddenly connect the two ends of the coil of the galvanometer? Is it correct to say that an emf is induced (in accordance to Lenz's law), and a current is produced such that a magnetic field is produced, that leads to no torque acting on the coil, and the oscillation stops?
Not very sure about this.
What would exactly happen?

Best Answer

[…] say I deflect it and release it. The coil should start oscillating.

Regular current meters are damped in order to get a sensible readout, I am not sure how much damping would be in such a galvanometer, probably a lot less. So it might oscillate freely for a while.

But now, what if I suddenly connect the two ends of the coil of the galvanometer.

From energy conservation one can estimate that the oscillation will die out quickly because the wire has a low resistance and will therefore burn a lot of power, quickly converting the kinetic/potential energy of the coil into heat.

Is it correct to say that an emf is induced (in accordance to Lenz's law) […]

The EMF is always there, even without the wire connecting the ends. It is just a voltage. There was no current before because there was no wire.

[…] and a current is produced such that a magnetic field is produced […]

Yes. The wire allows the already existing voltage to drive a current now.

[…] such that a magnetic field is produced […]

And that magnetic field will be opposing the external field that the coil is embedded in.

[…] that leads to no torque acting on the coil, and the oscillation stops?

If there was no torque, the oscillation would continue. The stopping of the oscillation is done by torque that is opposing the current direction of rotation.

I'd say that the opposing magnetic field that is created by allowing the current to flow will create a torque which opposes the rotation and therefore lets the oscillation die out.