Sully uses a battery and a coil of wire to create an electromagnet. using the same materials, if he wants to increase the strength of his electromagnet, he (must decrease increase not change) the number of loops in the coil of wire along its length. if he uses an additional battery, the strength of his electromagnet will (decrease increase remain the same ).

if he wants to increase the strength of his electromagnet, he must increase  the number of loops in the coil of wire along its length. If he uses an additional battery, the strength of his electromagnet will increase.

Explanation:

The equation that relates the variables in interest is:

B = μ*N*I/L

B = strength of the magnetic field

n = number of loops  in the coil of wire

I = current in the wire

μ =  magnetic permeability

L = length of coil of wire

Then, if the number of loops  increases, the strength of the electromagnet also increase.

An additional battery will cause an increment of the current in the wire , and therefore an increment of the strength of the electromagnet.

are their multiple choices ?

explanation:

unlike poles attract