Question

Read the passage about Andreas.
 

Andreas has to make an electromagnet in his science class. He was only given a nail, copper wire, and a 9-volt battery. The assignment was to make a magnet strong enough to pick up paper clips. His teacher decided to make the assignment into a competition to see whose magnet could pick up the most clips.

What can Andreas do to his magnet to make sure he wins by picking up the most paper clips?

A.
Andreas can wrap few coils of the wire, close together, around the nail.

B.
Andreas can wrap many coils of the wire, close together, around the nail.

C.
Andreas can wrap few coils of the wire, far apart, around the nail.

D.
Andreas can wrap many coils of the wire, far apart, around the nail.

Answer 1

B. Andreas can wrap many coils of the wire, close together, around the nail.

Reason: the magnetic field of a solenoid (and thus the electromagnet) is proportional to the number of turns times the current (N·I) and is stronger when the turns are close together so the field lines add. More, tightly spaced coils concentrate and strengthen the field, allowing the nail to pick up more paper clips.