e
tr
.X
w
w
w
Recommended Prior Knowledge It is essential that A2 Unit 3 is studied before this Unit.
Context. This Unit is a continuation of the work on magnetic fields to study aspects of electromagnetic induction. An introduction to alternating current is
also included.
Outline. The concepts of flux and flux linkage are introduced so that electromagnetic induction may be studied. Aspects of alternating current are also
included.
Online Resources. In this Unit, repeated use is made of Java Applets. These are usually well animated programmes. It has been found preferable to use
one main source of computer programmes as both teachers and students can become familiar with the procedure for using the resource and are therefore
more likely to connect to the web. The set of animations using the web address http://surendranath.tripod.com do not contain any applets on electromagnetic
induction or a.c. but once this address has been found then the Applet menu labelled ‘OTHER’ enables Applets on this topic from other sources to be found.
There is no need to subscribe to Tripod, just ignore their adverts and click on to either the Applets Menu or the ‘Click here’ instruction about any problem with
the menu. In the Online Resources column reference will be made directly to different authors but payment is required for applets called ‘Physlets’.
Learning Outcomes
Candidates should be able to:
Suggested Teaching Activities
Online Resources
Other resources
Reference should be made to
the list of textbooks printed in
the Syllabus document. Note
that some texts are more
suitable as library reference
texts whilst others are more
suitable as student texts and, in
particular, the ‘endorsed’
textbook.
All examples of examination
questions are taken from 9702
papers.
23(a)
define magnetic flux and the weber.
23(b)
recall and solve problems using  = BA.
It is helpful to use the alternative unit for
-2
magnetic flux density (A2 Unit 3) – Wb m
and to model field strength as the number
of magnetic field lines normal to unit area.
23(c)
define magnetic flux linkage.
It may be advantageous to consider 23(c)
as part of 23(d).
om
.c
s
er
ap
eP
m
A2 Physics UNIT 4 Electromagnetic Induction and a.c.
Learning Outcomes
Candidates should be able to:
23(d)
23(e)
23(f)
Suggested Teaching Activities
Online Resources
infer from appropriate experiments on
electromagnetic induction:
 that a changing magnetic flux can
induce an e.m.f. in a circuit,
Demonstrations should include:
moving a wire between the poles of a
horseshoe magnet,
moving a wire in the region of a magnet,
moving a magnet in/out of a coil,
moving a coil in the region of a magnet,
switching a current on/off in a coil, inducing
an e.m.f. in a second coil,
using a ferrous core in the coils.
http://webphysics.davids
on.edu/physlet
then go to
Part 5:
Electromagnetism and
on to Chapter 29:
Faraday’s Law.
 that the direction of the induced e.m.f.
opposes the change producing it,
The demonstrations above allow the
direction of the induced current to be
determined so that it can be deduced that a
magnetic field is induced that tends to
oppose the change. This is formalised as
Lenz’s law .
 the factors affecting the magnitude of
the induced e.m.f.
Consideration of the speed at which
components are moved enables the above
demonstrations to be used to deduce that
rate of cutting of flux is the important factor.
Flux linkage should be introduced.
Faraday’s law is the formal statement.
recall and solve problems using Faraday’s
law of electromagnetic induction and Lenz’s
law.
e.g. aircraft wing
change of flux in a coil
closing a metal window
explain simple applications of
electromagnetic induction.
e.g. mutual inductance  transformer
shaver socket
moving coil a.c. generator (no theory)
electromagnetic braking
Other resources
May 2010, Paper 41, q.5(b)
May 2009, Paper 4, q.7
May 2008, Paper 4, q.6(c)
May 2002, paper 4, q.6(a)
http://www.walterfendt.de/ph14e
then go to
Electrodynamics and on
to Generator
Nov 2002, Paper 4, q.7(a)
Learning Outcomes
Candidates should be able to:
Suggested Teaching Activities
Online Resources
http://www.walterfendt.de/ph14e
then go to
Electrodynamics and on
to Simple AC circuits
24(a)
show an understanding of and use the
terms period, frequency, peak value and
root-mean-square value as applied to an
alternating current or voltage.
Students should appreciate that the r.m.s.
value (rating) of an alternating current is
that value of the direct current that
produces thermal energy in a resistor at the
same rate as the alternating current.
24(d)
distinguish between r.m.s. and peak values
and recall and solve problems using the
relationship I = I 0 / 2 for the sinusoidal
case.
The insulation required on a 240 V mains
cable should be calculated
24(b)
deduce that the mean power in a resistive
load is half the maximum power for a
sinusoidal alternating current.
24(c)
represent a sinusoidally alternating current
or voltage by an equation of the form
x = x 0 sint.
24(e)
24(f)
show an understanding of the principle of
operation of a simple laminated iron-cored
transformer and recall and solve problems
using N s /N p = V s /V p = I p /I s for an ideal
transformer.
show an appreciation of the scientific and
economic advantages of alternating current
and of high voltages for the transmission of
electrical energy.
The fact that this may be considered as
another form of oscillation should be
discussed.
This should be considered as an example
of e.m. induction. The input and output
frequencies and phase difference should be
discussed.
It should be understood that the relations
are a consequence of no loss in flux and
100% efficiency.
This may be approached as a discussion
and should include power losses in
transmission at high/low voltages,
ease of changing voltage in home etc
24(g)
distinguish graphically between half-wave
and full-wave rectification.
The waveforms should be shown on a c.r.o.
24(h)
explain the use of a single diode for the
half-wave rectification of an alternating
current.
Only the use of ideal diodes is expected.
Other resources
May 2010, Paper 42, q.1(a)(b)
9702/4 May 02, 6(b)
http://webphysics.davids
on.edu/physlet
then go to Part 5:
Electromagnetism and
on to Chapter 31: AC
Circuits.
http://micro.magnet.fsu.
edu/electromag/java/ind
ex.html
then to ‘How a
transformer works’
May 2010, Paper 42, q.1(c)
May 2010, Paper 42, q.1(b)
Nov 2002, Paper 4, q.7(b)
May 2010, paper 41, q.6(b)
Oct 2009, Paper 42,q.6(a)(b)
Oct 2009, Paper 42,q.6(c)
Learning Outcomes
Candidates should be able to:
Suggested Teaching Activities
24(i)
explain the use of four diodes (bridge
rectifier) for the full-wave rectification of an
alternating current.
Candidates are expected to be able to draw
a bridge-rectifier circuit.
24(j)
analyse the effect of a single capacitor in
smoothing, including the effect of the value
of capacitance in relation to the load
resistance.
It is not expected that students will
understand the concept of time constant
CR. However, it is useful for them to know
that, for smooth d.c., CR should be much
larger than the period of the alternating
waveform.
Online Resources
Other resources
May 2010, Paper 41, q.5(a)
Oct 2009, Paper 41, q.7(a)(b)
May 2002, Paper 4, q.6(b)
Oct 2009, Paper 41, q.7(c)
May 2002, Paper 2, q.6(b)