Electromagnetism

A student moved a compass near the wires of the power lines next to a house. The compass needle then changed direction. The compass needle moved because

.

• an electric field surrounded the wires.

• a magnetic field surrounded the house.

• an electrical current produced in the wires stopped.

• a magnetic field was produced by the electric current.

Scientists have created trains that use magnets to make the trains float above the tracks as they travel. These trains float because

• the track is waxed.

• the like poles repel.

• the train has a low density.

• a chemical change occurs.

Which change will most likely increase the strength of a magnetic field produced by an electromagnet?

• Reduce the number of turns of the coil.

• Increase the voltage of a battery.

• Remove the iron nail.

• Switch the direction in which the battery is connected.

Which of the following statements best describes an electric generator?

• A magnet is rotated through a coil of wire to produce an electric current.

• Electric potential in a rotating coil of wire creates a permanent magnet.

• An electrical current causes a coil of wire to rotate in a magnetic field.

• Forces from a permanent magnet allow a coil of wire to rotate.

An electric motor transforms _______________ energy into ________________ energy.

• electrical, chemical

• mechanical, electrical

• mechanical, chemical

• electrical, mechanical

Which of the pictures shows an electric motor?

• A

• B

Which of the pictures below shows an electric generator?

• A

• B

What happens to the direction of the magnetic field around a wire if the electric current moving through the wire is reversed?

• It reverses direction.

• It stays the same.

• It does not have a direction.

• The magnetic field stops

A worker at a scrap metal yard had to move pieces of iron from one side of the yard to the other side of the yard using an electromagnet. After easily moving some of the smaller pieces of iron, he could not get a larger piece of iron to stay attracted to the electromagnet because it was too heavy. Since he is using an electromagnet, which of the following could he do to strengthen the electromagnet’s magnetic field in order to lift the large piece of iron?

• decrease the number of coils of wire in the solenoid

• increase the electric current moving in the solenoid

• use a smaller iron core

• He cannot change the electromagnet’s strength.

What kind of magnet can be turned on and off? (Man-made magnet)

• refrigerator magnet
• electromagnet
• magnetite
• iron