Notes

6.6.1.2 Properties of waves

Students should be able to describe wave motion in terms of their
amplitude, wavelength, frequency and period.

The amplitude of a wave is the maximum displacement of a point
on a wave away from its undisturbed position.

The wavelength of a wave is the distance from a point on one wave
to the equivalent point on the adjacent wave.

The frequency of a wave is the number of waves passing a point
each second.

MS 1c, 3b, c
period = 1
f requency
T =
1
f
period, T, in seconds, s
frequency, f, in hertz, Hz

The wave speed is the speed at which the energy is transferred (or
the wave moves) through the medium.

All waves obey the wave equation:
MS 1c, 3b, c

Students should be able to
apply this equation which is
given on the Physics
equation sheet.

wave s peed = f requency × wavelength

v = f λ

wave speed, v, in metres per second, m/s
frequency, f, in hertz, Hz

wavelength, λ, in metres, m

Students should be able to:

• identify amplitude and wavelength from given diagrams
MS 1c, 3b, 3c
Students should be able to
recall and apply this
equation.

• describe a method to measure the speed of sound waves in
air

• describe a method to measure the speed of ripples on a water
surface.

Required practical activity 20: make observations to identify the suitability of apparatus to
measure the frequency, wavelength and speed of waves in a ripple tank and waves in a solid and
take appropriate measurements.

6.6.2 Electromagnetic waves

6.6.2.1 Types of electromagnetic waves

Electromagnetic waves are transverse waves that transfer energy
from the source of the waves to an absorber.

Electromagnetic waves form a continuous spectrum and all types of
electromagnetic wave travel at the same velocity through a vacuum
(space) or air.

The waves that form the electromagnetic spectrum are grouped in
terms of their wavelength and their frequency. Going from long to
short wavelength (or from low to high frequency) the groups are:

radio, microwave, infrared, visible light (red to violet), ultraviolet, Xrays and gamma rays.
Our eyes only detect visible light and so detect a limited range of
electromagnetic waves.

Students should be able to give examples that illustrate the transfer
of energy by electromagnetic waves.

6.6.2.2 Properties of electromagnetic waves 1

(HT only) Different substances may absorb, transmit, refract or
reflect electromagnetic waves in ways that vary with wavelength.

(HT only) Some effects, for example refraction, are due to the
difference in velocity of the waves in different substances.

Students should be able to construct ray diagrams to illustrate the
refraction of a wave at the boundary between two different media.

(HT only) Students should be able to use wave front diagrams to
explain refraction in terms of the change of speed that happens
when a wave travels from one medium to a different medium.

Required practical activity 21: investigate how the amount of infrared radiation absorbed or
radiated by a surface depends on the nature of that surface.

6.6.2.3 Properties of electromagnetic waves 2

(HT only) Radio waves can be produced by oscillations in electrical
circuits.

(HT only) When radio waves are absorbed they may create an
alternating current with the same frequency as the radio wave itself,
so radio waves can themselves induce oscillations in an electrical
circuit.

Changes in atoms and the nuclei of atoms can result in
electromagnetic waves being generated or absorbed over a wide
frequency range. Gamma rays originate from changes in the
nucleus of an atom.

Ultraviolet waves, X-rays and gamma rays can have hazardous
effects on human body tissue. The effects depend on the type of
radiation and the size of the dose. Radiation dose (in sieverts) is a
measure of the risk of harm resulting from an exposure of the body
to the radiation.

1000 millisieverts (mSv) = 1 sievert (Sv)
Students will not be required to recall the unit of radiation dose.
Students should be able to draw conclusions from given data about
the risks and consequences of exposure to radiation.

Ultraviolet waves can cause skin to age prematurely and increase
the risk of skin cancer. X-rays and gamma rays are ionising
radiation that can cause the mutation of genes and cancer.

6.6.2.4 Uses and applications of electromagnetic waves

Electromagnetic waves have many practical applications. For
example:

• radio waves – television and radio

• microwaves – satellite communications, cooking food

• infrared – electrical heaters, cooking food, infrared cameras

• visible light – fibre optic communications

• ultraviolet – energy efficient lamps, sun tanning

• X-rays and gamma rays – medical imaging and treatments.

(HT only) Students should be able to give brief explanations why
each type of electromagnetic wave is suitable for the practical
application.

(HT only) WS 1.4

6.7 Magnetism and electromagnetism
Electromagnetic effects are used in a wide variety of devices. Engineers make use of the fact that
a magnet moving in a coil can produce electric current and also that when current flows around a
magnet it can produce movement. It means that systems that involve control or communications
can take full advantage of this.

6.7.1 Permanent and induced magnetism, magnetic forces and fields

6.7.1.1 Poles of a magnet

The poles of a magnet are the places where the magnetic forces
are strongest. When two magnets are brought close together they
exert a force on each other. Two like poles repel each other. Two
unlike poles attract each other. Attraction and repulsion between
two magnetic poles are examples of non-contact force.

A permanent magnet produces its own magnetic field. An induced
magnet is a material that becomes a magnet when it is placed in a
magnetic field. Induced magnetism always causes a force of
attraction. When removed from the magnetic field an induced
magnet loses most/all of its magnetism quickly.

Students should be able to describe:
• the attraction and repulsion between unlike and like poles for
permanent magnets

• the difference between permanent and induced magnets.

6.7.1.2 Magnetic fields

The region around a magnet where a force acts on another magnet
or on a magnetic material (iron, steel, cobalt and nickel) is called
the magnetic field.

The force between a magnet and a magnetic material is always one
of attraction.

The strength of the magnetic field depends on the distance from the
magnet.

The field is strongest at the poles of the magnet.
The direction of the magnetic field at any point is given by the
direction of the force that would act on another north pole placed at
that point.

The direction of a magnetic field line is from the north
(seeking) pole of a magnet to the south(seeking) pole of the
magnet.

A magnetic compass contains a small bar magnet. The Earth has a
magnetic field. The compass needle points in the direction of the
Earth’s magnetic field.

Students should be able to:

• describe how to plot the magnetic field pattern of a magnet
using a compass

• draw the magnetic field pattern of a bar magnet showing how
strength and direction change from one point to another

• explain how the behaviour of a magnetic compass is related
to evidence that the core of the Earth must be magnetic.

6.7.2 The motor effect

6.7.2.1 Electromagnetism

When a current flows through a conducting wire a magnetic field is
produced around the wire. The strength of the magnetic field
depends on the current through the wire and the distance from the
wire.

Shaping a wire to form a solenoid increases the strength of the
magnetic field created by a current through the wire. The magnetic
field inside a solenoid is strong and uniform.

The magnetic field around a solenoid has a similar shape to that of
a bar magnet. Adding an iron core increases the strength of the
magnetic field of a solenoid. An electromagnet is a solenoid with an
iron core.

Students should be able to:

• describe how the magnetic effect of a current can be
demonstrated

• draw the magnetic field pattern for a straight wire carrying a
current and for a solenoid (showing the direction of the field)

• explain how a solenoid arrangement can increase the
magnetic effect of the current.


6.7.2.2 Fleming's left-hand rule (HT only)


When a conductor carrying a current is placed in a magnetic field
the magnet producing the field and the conductor exert a force on
each other. This is called the motor effect.

Students should be able to show that Fleming's left-hand rule
represents the relative orientation of the force, the current in the
conductor and the magnetic field.

Students should be able to recall the factors that affect the size of
the force on the conductor.

AQA GCSE Combined Science: Trilogy 8464. GCSE exams June 2018 onwards. Version 1.1 04 October 2019
Visit aqa.org.uk/8464 for the most up-to-date specification, resources, support and administration 161

For a conductor at right angles to a magnetic field and carrying a
current:

f orce = magnetic f lux density × current × length
F = B I l
force, F, in newtons, N
magnetic flux density, B, in tesla, T
current, I, in amperes, A (amp is acceptable for ampere)
length, l, in metres, m
MS 3b, c

Students should be able to
apply this equation which is
given on the physics
equation sheet.

6.7.2.3 Electric motors (HT only)

A coil of wire carrying a current in a magnetic field tends to rotate.
This is the basis of an electric motor.

Students should be able to explain how the force on a conductor in
a magnetic field causes the rotation of the coil in an electric motor.


6.8 Key ideas

The complex and diverse phenomena of the natural and man-made world can be described in
terms of a small number of key ideas in physics.

These key ideas are of universal application, and we have embedded them throughout the subject
content. They underpin many aspects of the science assessment and will therefore be assessed
across all papers.

Key ideas in physics:

• the use of models, as in the particle model of matter or the wave models of light and of sound
• the concept of cause and effect in explaining such links as those between force and
acceleration, or between changes in atomic nuclei and radioactive emissions
• the phenomena of ‘action at a distance’ and the related concept of the field as the key to
analysing electrical, magnetic and gravitational effects
• that differences, for example between pressures or temperatures or electrical potentials, are
the drivers of change
• that proportionality, for example between weight and mass of an object or between force and
extension in a spring, is an important aspect of many models in science
• that physical laws and models are expressed in mathematical form.