Which of the following cannot induce a voltage in a loop of wire?

Expanding or contracting the loop in a region where there is no magnetic field.


Moving the loop near a magnet.


Moving a magnet near the loop


Changing the current in a nearby loop.

Which of the following cannot induce a voltage in a loop of wire?
A (the first one)


you need a changing magnetic field to induce a voltage.


B the wire is moving through the magnetic field so it is changing


C the magnet is moving so exactly the same as B, the wire does not know if it is moving or the magnet is moving it is all relative!!


D an electric current produces a magnetic field, and changing current produces a changing magnetic field





So in all but the first one the magnetic field is changing with respect to the wire.
Reply:expanding and contracting a loop with no magnetic field is going to induce the least voltage.....technically there will still be some voltage as you are still moving copper through a magnetic feild (the earths) but that is so minimal, it doesn't count.





moving the loop near a magnet and moving a magnet near the loop is the same thing, and will make voltage, as you have a conductor cutting through magnetic flux lines.





changing current in a nearby loop is the basis of transformer action and will make voltage



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