Magnetism & Electromagnetism — Drills · Grade 12 Science

Chapter: Electricity, Magnetism & Circuits

What these drills covers

By the end of Magnetism & Electromagnetism you should be able to:

6 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: magnetic field, electromagnet, electromagnetic induction, electric motor, generator.

Problem 1

The region around a magnet where it exerts a force is called its:
  1. sound field
  2. magnetic field
  3. electric field
  4. gravitational field
Answer and explanation

magnetic field

The magnetic field is the region around a magnet (or a current) where magnetic forces act.

Problem 2

An electric motor converts electrical energy into:
  1. light energy
  2. sound energy
  3. mechanical (motion) energy
  4. chemical energy
Answer and explanation

mechanical (motion) energy

A motor uses the force on a current-carrying coil in a magnetic field to produce motion.

Problem 3

To induce a current in a coil of wire, you must:
  1. cool the coil down
  2. charge it with static electricity
  3. hold a magnet still nearby
  4. change the magnetic field through the coil
Answer and explanation

change the magnetic field through the coil

Electromagnetic induction requires a changing magnetic field; a stationary field produces no current.

Problem 4

A wire 0.4 m long carries 3 A perpendicular to a uniform 0.5 T magnetic field. Find the force on it. (F = BIL)
Answer and explanation

0.6 N

F = BIL = 0.5 × 3 × 0.4 = 0.6 N. The BIL form applies because current and field are perpendicular; otherwise include sinθ.

Problem 5

Name one everyday device that uses electromagnetic induction and briefly explain how it uses it.
Answer and explanation

A generator (for example in a wind turbine or power plant) uses electromagnetic induction: spinning a coil inside a magnetic field constantly changes the field through the coil, inducing a voltage that drives current. Other valid answers include transformers, induction cooktops, and wireless phone chargers, all of which rely on a changing magnetic field inducing a current.

Problem 6

A generator is essentially:
  1. a motor run in reverse, turning motion into electricity
  2. an insulating device
  3. a battery that stores charge
  4. a large resistor
Answer and explanation

a motor run in reverse, turning motion into electricity

A generator has the same parts as a motor but runs in reverse: instead of using electricity to make motion, it uses motion to induce electricity.

Browse all courses