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how exactly does changing magnetic flux result in current induced

yeah I get the whole explanation of moving a magnet in a coil but then most sources just say "current is then induced" how? or am I just supposed to get it that way?

Reply 1

Eimmanuel

Study Forum Helper

Original post by sarah99630

yeah I get the whole explanation of moving a magnet in a coil but then most sources just say "current is then induced" how? or am I just supposed to get it that way?

As a magnet is moving toward a coil, there is a change in the magnetic flux linkage with the coil. The change in magnetic flux linkage would “give rise” to an induced e.m.f. according to Faraday’s law. This induced e.m.f. will result in having an induced current in the coil.

Recall that a battery would provide the emf in a circuit to cause the current to flow in the circuit.

Reply 2

sarah99630

Original post by Eimmanuel

ahaa i get it thanks!! so for an emf to be induced it does not need a complete circuit, but for a current there has to be a battery right?

Reply 3

uberteknik

Original post by sarah99630

ahaa i get it thanks!! so for an emf to be induced it does not need a complete circuit

Correct. For an open circuit, the changing flux forces electrons in the conductor to bunch up at one end of the conductor. There will be a momentary flow of current as electrons still move within the limited length of the conductor, but they cannot move further than the end. So at one end there will be a deficit of electrons (net +ve charge build up) and at the other end there will be a surplus of electrons (net -ve charge build up). The difference of charge measured across the ends of the conductor is the e.m.f.

That e.m.f build up, is the pressure that provides the potential energy (hence voltage potential) to push electrons around a closed circuit.

,but for a current there has to be a battery right?

Noooooo. A battery is one way of providing an emf.
However, as I explained above, it's not the only way. If the conductor experiencing a changing magnetic flux is part of a closed loop, then current will flow around the loop.

Perform a thought experiment:

Think of a bicycle where the chain is a conductor full of electrons. If the cycle is secured to a post, then trying to pedal away will not result in motion, the pedal force (changing magnetic flux) simply applies pressure (emf) to the chain but it cannot move.

Only when the cycle is not secured, will the chain move freely in a loop and work can be performed.

(edited 6 years ago)

Reply 4

Eimmanuel

Study Forum Helper

Original post by sarah99630

ahaa i get it thanks!! so for an emf to be induced it does not need a complete circuit, but for a current there has to be a battery right?

We don't need to have a complete circuit to have induced emf but complete circuit is required for induced current like closed loop coil.

For example, when you drop a magnet through a coil of wire, there will be induced emf and induced current in the coil.
Watch the following video to see that the LED light up for a short while when the magnet falls through the coil.
https://www.youtube.com/watch?v=Fc1pfeheZ74&pbjreload=10

But if the magnet is dropped through a loop that has an opening (as shown in the picture below on the right), there is will be induced emf but no induced current because of the open circuit.

We don’t need a battery source to have induced current.

You can think of the flow of “concepts” as follow:

Changing magnetic flux linkage --> Induced emf --> Induced current provided it is a closed circuit.