Which of the following will cause an induced current in a coil of wire?

the constant field of the earth passing through the coil
a magnet resting near the coil
a magnet being moved into or out of the coil
a wire carrying a constant current near the coil

The answer is b.)

Explanation:

The following are given as causes for an induced current in a coil of wire:

a. ) a magnet resting near the coil.

    - This not true as there will be no change in flux. Only a change in flux  

       will lead to the production of an induced current.

b.) a magnet being moved into or out of the coil.

   - This is TRUE .  This will lead to a change in flux which will lead to the  

      production of an induced current.

c.) constant current flowing through a wire placed near the coil.

    - This is not true as there will not be any change in flux.  

resonant frequency

so easy. just google the electromagnetic waves and it’ll pop up.