Question

Counter electromotive force happens as a result of a change in a magnetic field?

Answer 1

Meaning when a electromagnet repels a magnet.
The CEMF only happens when the magnet is "repelled" its a result a aftermath of the force being applied.

Answer 2

@Shane_B

Answer 3

note that the electromotive force(which moves electrons) tries to oppose the magnetic field producing it as a result of newton's third law, but it cannot repel the magnet as it is an internal force.

Answer 4

i dunno exactly what you mean by counter emf

but when magnetic field changes it would induce an emf which tries to negate the effect of the change!..

Answer 5

I would say the term "counter-emf" is relevant to the study of motors. So I think it is relevant in the context of a conductor moving in a stationary field, not so much so in the context of a change in magnetic field.

Answer 6

So generally EMF is only induced when there is a change in a magnetic field.
Examples of change is:
Motion of a magnet
Creation/destruction of a magnetic field
What else?

Answer 7

@Shadowys what do you mean? if a magnet passes a coil its KE is converted. Thus the magnet "slows" down.
Example:
Drop a magnet in a copper pipe.

Answer 8

@Mashy yea, what other factors could cause "Change" other than motion of a magnet? I already mentioned the creation/destruction of a magnetic field induced EMF too.

Answer 9

Careful: if the magnet slows down, it has nothing to do with emf or counter-emf.

Remember emf is a misleading term for the voltage of an induced battery, and has nothing to do with a mechanical force.

emf expressed in volts
real force expressed in newtons

Answer 10

@Vincent-Lyon.Fr Please explain!

If the magnet speeds up or slow's down it has nothing to do with c-emf? Or emf itself?!?!

Answer 11

I'm confused... at the point you've stated @Vincent-Lyon.Fr

Answer 12

I know that when a magnet passes through a coil, it induced emf that opposes the applied emf from the power source.
It also created a magnetic field that opposes the magnet.

Answer 13

other ways is to rotate a coil in a stationary field..

and another way is having an alternating or changing current which also produce changing magnetic fields and hence lead to induction!

Answer 14

Hello

Answer 15

If there is an open circuit not closed.
And a magnet passes through a coil, emf is induced but current can not flow.
What happens?

Answer 16

The magnet is moving back and forth.
And there is induced emf. However, because the circuit is opened, I = 0
is this correct?

If so, when the magnet stops V = 0. As soon as the magnet is at rest voltage drops rapidly(some what being instant and un-noticeable)