Open the simulation Print this page on A4.

Student worksheet

4. Electromagnetism & Induction

Name:

Class: ______ Date: ________

Open the simulation and work through each chapter. Write your prediction before you run the test.

a. Magnetic fields

Predict

A compass sits beside a wire carrying current out of the page. Predict what the needle does when the current is reversed.

My prediction (and why)

What happened

Was I right? If not, what was wrong with my thinking?

Test: recording table

Source	Current direction	Sketch of field lines

Pattern I found:

Challenge

Two N poles face each other. Find the neutral point, where the two fields cancel and the compass is not pushed either way. Drag the compass there.

My solution

Exam practice

Which material is best for the core of an electromagnet that must be switched on and off? [1]
A Steel
B Soft iron
C Copper
D Aluminium
Answer: ____
In which direction do magnetic field lines point outside a bar magnet? [1]
A From S to N
B From N to S
C From the middle outwards
D Towards the middle
Answer: ____
Current flows into the page in a straight wire. Viewed from above the page, the field lines are… [1]
A clockwise circles
B anticlockwise circles
C straight lines parallel to the wire
D straight lines radiating out
Answer: ____

b. Force on a current in a field

Predict

Field left → right, current into the page. Predict the direction of the force.

My prediction (and why)

What happened

Was I right? If not, what was wrong with my thinking?

Test: recording table

Field direction	Current direction	Force direction

Pattern I found:

Challenge

Find two different settings of current direction and field direction that push the wire upwards.

My solution

Exam practice

A wire carries current into the page between a N pole on the left and a S pole on the right. Which way is the force on the wire? [1]
A Up the page
B Down the page
C Towards N
D Towards S
Answer: ____
The current in the wire and the magnetic field are both reversed. What happens to the force? [1]
A It reverses
B It is unchanged
C It becomes zero
D It doubles
Answer: ____
Which change does NOT increase the force on a current-carrying wire in a magnetic field? [1]
A Increasing the current
B Using a stronger magnet
C Reversing the current
D Making a longer length of wire lie in the field
Answer: ____

c. The d.c. motor

Predict

Predict what the coil does if the split-ring commutator is replaced by slip rings.

My prediction (and why)

What happened

Was I right? If not, what was wrong with my thinking?

Test: recording table

Turns	Current / A	Magnet	Core	Speed / rpm

Pattern I found:

Challenge

Make the motor turn clockwise at more than 150 rpm.

My solution

Exam practice

What is the purpose of the split-ring commutator in a d.c. motor? [1]
A To make the current larger
B To reverse the current in the coil every half-turn so the coil keeps turning the same way
C To make the magnet stronger
D To change d.c. into a.c. in the supply
Answer: ____
Which change would make a d.c. motor turn in the opposite direction? [1]
A Doubling the current
B Reversing the battery
C Adding more turns
D Adding a soft-iron core
Answer: ____
In which position of the coil is the turning effect zero? [1]
A Coil plane parallel to the field
B Coil plane at right angles to the field
C At every position
D Coil at 45° to the field
Answer: ____

d. Electromagnetic induction

Predict

Pushing N in gives a right deflection. Predict the needle when the magnet is held still inside the coil.

My prediction (and why)

What happened

Was I right? If not, what was wrong with my thinking?

Test: recording table

Movement	Speed	Turns	Magnet	Peak e.m.f. / mV	Direction of deflection

Pattern I found:

Challenge

Make the galvanometer needle swing to the left by at least 4.0 mV.

My solution

Exam practice

A magnet rests inside a coil connected to a galvanometer. What does the galvanometer read? [1]
A A steady current
B Zero
C A current that keeps reversing
D A current that slowly increases
Answer: ____
Which change does NOT increase the e.m.f. induced when a magnet is pushed into a coil? [1]
A Pushing it in faster
B Using more turns
C Using a stronger magnet
D Using a thicker wire with the same number of turns
Answer: ____
The N pole of a magnet is pulled out of a coil. What pole is induced at the end of the coil nearest the magnet? [1]
A N, to repel the magnet
B S, to attract the magnet back
C No pole
D Both N and S
Answer: ____

e. The a.c. generator

Predict

Generator at 2 rev/s gives 2.4 V peak at 2 Hz. Predict the output at 4 rev/s.

My prediction (and why)

What happened

Was I right? If not, what was wrong with my thinking?

Test: recording table

rev/s	Turns	Connection	Peak / V	Frequency / Hz

Pattern I found:

Challenge

Set up the generator to give an a.c. output with a peak of 6.0 V and a frequency of 5 Hz.

My solution

Exam practice

In a simple a.c. generator, when is the induced e.m.f. zero? [1]
A When the plane of the coil is parallel to the field
B When the plane of the coil is at right angles to the field
C When the coil turns fastest
D Never
Answer: ____
What is the job of the slip rings in an a.c. generator? [1]
A To reverse the output every half-turn
B To keep each end of the coil connected to the same brush
C To make the field stronger
D To make the output d.c.
Answer: ____
A generator’s output has a period of 0.020 s. What is its frequency? [1]
A 0.020 Hz
B 20 Hz
C 50 Hz
D 200 Hz
Answer: ____

f. Transformers

Predict

Np = 1000, 230 V a.c. on the primary. Predict Vs when Ns = 50.

My prediction (and why)

What happened

Was I right? If not, what was wrong with my thinking?

Test: recording table

Np	Ns	Vp / V	Vs / V	Ns/Np	Vs/Vp

Pattern I found:

Challenge

Design a transformer that gives 12 V a.c. from the 230 V mains (for a model railway).

My solution

Exam practice

A transformer has 2000 turns on its primary and 100 turns on its secondary. The primary is connected to 230 V a.c. Calculate the secondary p.d. [2]
An ideal transformer steps 230 V down to 6.0 V. The secondary current is 2.3 A. Calculate the primary current. [2]
Why will a transformer not work with a steady d.c. supply? [1]
A d.c. is too small
B A steady current gives a magnetic field that does not change, so no e.m.f. is induced
C The core would melt
D d.c. cannot flow in a coil
Answer: ____