Question

The telegraph was one of the first machines that could send a message almost instantly to someone hundreds of miles away. The telegraph used a current to turn an electromagnet on and off. When the electromagnet was on it was attracted to a metal plate and it would tap. A series of taps was used to send a message.

How can a current in a wire be used to make an electromagnet?
A.
wrap the wire around a magnet
B.
wrap the wire around a piece of iron
C.
hold a magnet just touching the wire
D.
add a stronger battery to the wire

Answer 1

B.

Wrapping the wire into a coil around a piece of iron (an iron core) makes an electromagnet: current through the coil produces a magnetic field, and the iron concentrates and strengthens that field. The other options don't produce an electromagnet by themselves.