Which does not increase the strength of an electromagnet?

a. more current in the solenoid

b. using a “soft iron” core

c. fewer turns in the coil

d. more turns in the coil

The correct answer is "fewer turns in the coil".

Explanation:

Electromagnet: It is not a permanent magnet. When the current passes through iron core wounded by the coils then it will get magnetized.

The domains of the electromagnet gets aligned.

It will loose its magnetism easily when the current is not flowing in it. It is a temporary magnet.

In the electromagnet, the strength of the magnetism can be increased or decreased by increasing the number of turns in the coil or by using a soft iron core and by increasing the current.

Therefore, the correct option is (C).