Magnetism and Electromagnetism — High School Physics practice questions

The magnetic field around a straight current-carrying wire forms:

1. circles around the wire
2. straight lines along the wire
3. lines pointing away from the wire
4. a uniform field pointing north

Answer: A — circles around the wire

A) Correct — Use the right-hand rule to find the direction. B) Is not the pattern. C) Is the electric field of a charge. D) Confuses it with Earth's field; a wire's field circles it.

The north end of a compass needle points toward geographic north because:

1. Earth's magnetic north pole is near geographic north
2. Earth's magnetic south pole is near geographic north
3. the needle is pulled by the North Star
4. the needle is pulled by gravity

Answer: B — Earth's magnetic south pole is near geographic north

B) Correct — Opposite poles attract. A) Would repel the needle's north end. C) Stars don't affect compasses. D) Gravity doesn't orient compasses.

An electric motor converts:

1. mechanical energy into electrical energy
2. heat into electrical energy
3. sound into electrical energy
4. electrical energy into mechanical energy

Answer: D — electrical energy into mechanical energy

D) Correct — Current in a magnetic field feels a force. A) Is a generator. B) Is a thermocouple. C) Is a microphone.

An electric generator converts:

1. electrical energy into mechanical energy
2. chemical energy into electrical energy
3. mechanical energy into electrical energy
4. light into electrical energy

Answer: C — mechanical energy into electrical energy

C) Correct — Spinning coils in a magnetic field induce current. A) Is a motor. B) Is a battery. D) Is a solar cell.

Transformers work only with alternating current because:

1. DC is too strong
2. DC can't flow through wire coils
3. they need a changing magnetic field
4. AC has no voltage

Answer: C — they need a changing magnetic field

C) Correct — Steady DC produces no induction. A) Strength isn't the issue. B) It can. D) AC has voltage.

Outside a bar magnet, magnetic field lines run from:

1. north to south
2. south to north
3. the center outward
4. east to west

Answer: A — north to south

A) Correct — Inside the magnet they continue south to north. B) Is the direction inside the magnet. C) Is not the pattern. D) Isn't defined by compass directions.

Two magnets placed north pole to north pole will:

1. repel
2. attract
3. have no effect
4. become demagnetized

Answer: A — repel

A) Correct — Like poles repel. B) Opposite poles attract. C) Magnets exert forces. D) Not from simply approaching.

What is the force on a charge moving in a magnetic field?

F = qvB sin θ, perpendicular to both v and B (right-hand rule for direction).

State Faraday's Law of Induction.

EMF = −dΦ/dt. The induced EMF is proportional to the rate of change of magnetic flux.

Magnetic field lines around a bar magnet?

Outside the magnet they run from the north pole to the south pole and form closed loops. They are closest together, and the field strongest, near the poles. Like poles repel; unlike poles attract.