Lesson: Electromagnetic Induction Physics • 9th Grade

In this lesson, we will learn how to describe the electric current induced in a wire that is placed in a changing magnetic field.

Lesson Plan

Objectives

Students will be able to

recognize that a changing magnetic field will induce a current in a loop of wire,
recognize that a more rapidly changing magnetic field will induce a greater current,
recognize that a changing magnetic field can be achieved by moving a bar magnet toward or away from a wire,
recognize that it is the relative motion of a bar magnet and a wire that achieves the changing magnetic field,
state what a solenoid is,
recognize that for a solenoid, the potential difference across its ends produced by a changing magnetic field can be increased by increasing the number of turns in the solenoid,
recognize that an induced magnetic field always opposes that which induced it (Lenz’s law),
recognize that for a straight wire moving through a magnetic field, a potential difference will only be induced across it if it is not moving parallel or antiparallel to the field,
recognize that for a straight wire moving through a magnetic field, the potential difference induced across it will be at a maximum if it is moving perpendicular to the field,
relate diagrams showing the motion of a wire in a magnetic field to graphs of the potential difference across the wire against time.

Prerequisites

Students should already be familiar with

current,
potential difference,
bar magnets,
magnetic fields,
magnetic field lines.

Exclusions

Students will not cover

mathematical calculations of induced currents and potential differences,
generators,
electric motors.

Lesson Video

Sample Question Videos

03:38
03:45
03:57

Lesson Worksheet

Q1:

The direction of the current induced in a conductor by a changing is such that the magnetic field created by the induced current the initial changing magnetic field.

Q2:

The diagram shows a permanent magnet being moved through a loop of copper wire. This motion induces an electric current of 0.5 A in the wire.

If the magnet is moved through the loop at half the speed, what will the current in the loop be?

If the permanent magnet is changed for one that is twice as strong and moves through the loop at the original speed, what will the current in the loop be?

Q3:

Diagram (a) shows a straight piece of copper wire moving along a rectangular path in a uniform magnetic field. Diagram (b) shows the potential difference across the piece of wire against time as it does so. Position in diagram (a) corresponds to the section marked in diagram (b).

Which section of diagram (b) does position in diagram (a) correspond to?

Which position in diagram (a) does section in diagram (b) correspond to?