Lesson: Force on Conducting Wires in Magnetic Fields Physics • 9th Grade

In this lesson, we will learn how to use the formula F = BIL to calculate the force experienced by a current-carrying wire that has been placed in a uniform magnetic field.

Lesson Plan

Objectives

Students will be able to

recognize that if a current-carrying wire is placed in a magnetic field, there will be a force on it and it may move,
recognize that the wire must be placed perpendicular to the magnetic field for the magnitude of the force to be greatest,
recognize that if the wire is placed parallel to the field, there will be no force on it,
work out the direction of the force using Fleming’s left-hand rule,
use in all permutations.

Prerequisites

Students should already be familiar with

what electric current is,
the idea that permanent magnets can attract or repel each other,
what a force is.

Exclusions

Students will not cover

cases in which the angle between the wire and the field is neither nor ,
what happens in nonuniform magnetic fields/time-varying magnetic fields,
what happens when the wire is curved/anything other than straight,
what happens when the wire has an alternating current,
the effect of magnetic fields on charged particles/beams of charged particles,
torque on loops of wire.

Lesson Video

Sample Question Videos

01:45
02:23
01:41

Lesson Worksheet

Q1:

A 50 cm current-carrying section of wire is positioned at to a 0.2 T magnetic field. It experiences a force of 0.25 N. What is the strength of the electric current in the wire?

Q2:

The diagram shows a section of wire that has been positioned parallel to a uniform 0.1 T magnetic field. The wire carries a current of 2 A. What is the direction of the force acting on the wire due to the magnetic field?

Q3:

The diagram shows a section of wire that has been positioned at to a 0.1 T magnetic field. The wire carries a current of 2 A. What is the direction of the force acting on the wire due to the magnetic field?