WAVES AND RADIATION SAMPLE PACK
WAVES AND RADIATION SAMPLE PACK
This sample pack provides a selection of ideas and activities for secondary
science teachers for teaching about electromagnetic radiation, along with
some simple low-cost practical resources.
A family of radiations The electromagnetic spectrum covers a very wide range of frequencies. This
pack starts with the visible part of the spectrum, and then extends to infrared, microwave and
ultraviolet. The different kinds of electromagnetic radiation show differences in properties, but there
are also similarities in way they behave, so the spectrum can be seen as a ‘family of radiations’.
Making it relevant to pupils The electromagnetic spectrum is an abstract idea and needs to be
introduced carefully by stages, starting with what pupils are most familiar with – visible light. This pack
aims to provide activities that can connect to pupils’ lives and interests, and includes work on mobile
phones, computer displays, energy-efficient bulbs, remote controls, and other applications.
What’s in this pack? To help in identifying the practical resources they are divided into five bags. The
sequence of activities in this leaflet, and the accompanying practical resources are shown below.
Activities
Practical resources
The visible spectrum
Activity 1 Frequencies in the visible spectrum
Bag A: SEP Spectroscope
Activity 2 Combining colours
Activity 3 Signalling using fibre optics
Bag B: Visible radiation
Beyond the visible
Activity 4 Detecting infrared radiation
Activity 5 Signalling with infrared radiation
Bag C: Infrared radiation
Activity 6 Microwave radiation
Activity 7 Ultraviolet radiation
Bag D: Microwave and ultraviolet radiation
Wave properties of radiation
Activity 8 Diffraction
Activity 9 Polarisation
Bag E: Wave properties of radiation
Further information At the back of this booklet, there is information about how to obtain other SEP
curriculum resources to support the teaching of this topic, how to purchase further practical resources,
and where to find further ideas and suggestions.
© 2009 GATSBY SCIENCE ENHANCEMENT PROGRAMME
1
WAVES AND RADIATION SAMPLE PACK
BAG A: SEP SPECTROSCOPE
The contents of this bag:

The large bag includes instructions
on how to make a simple
spectroscope from the enclosed
black plastic cut-out and CD.
Activity 1 Frequencies in the visible spectrum
What this activity illustrates: A spectroscope can be used to observe the spectra of different sources of
light. What we perceive as ‘white’ light is actually made up of many different ‘colours’.
What you need from this pack: assembled spectroscope.
Other things you will need: access to a range of different lamps, e.g. conventional (incandescent) light
bulb, fluorescent strip, energy-saving light bulb.
What to do
Stand underneath a fluorescent light strip. Hold the spectroscope so that the slit at the top is pointing
towards the fluorescent light, and look through the hole on the side of the box. You should see a
spectrum. Point the spectroscope slit at a conventional light bulb, and observe the spectrum. Do you
notice any differences? Try looking at the spectra of other lamps.
Explanation
A traditional light bulb (an incandescent bulb) gives out radiation with a continuous range of
frequencies, and a spectroscope allows us to see this range. So what we perceive as ‘white’ light is in
fact a combination of many different ‘colours’. (An incandescent light also gives out much radiation in
the infrared region, though this is invisible to the naked eye.) A fluorescent lamp produces a different
kind of spectrum – rather than being continuous, it shows peaks of intensity at certain frequencies.
This is why the ‘white’ light from a fluorescent lamp appears different from an incandescent lamp.
N.B. The spiral track of closely spaced lines on the CD acts as a diffraction grating. A prism can also
be used to produce a spectrum in a similar way, but this is due to refraction (a rainbow is also
produced by refraction of light by water droplets in the air).
Other things to do
The spectroscope can be used to see how the ‘white’ light from a computer monitor is made up of red,
green and blue bands, and can be used outside to observe Fraunhofer lines (do not point directly at
the Sun).
© 2009 GATSBY SCIENCE ENHANCEMENT PROGRAMME
2
WAVES AND RADIATION SAMPLE PACK
BAG B: VISIBLE RADIATION
The contents of this bag:

3 LEDs (red, green and blue – note
that these LEDs have a similar
colourless appearance until they are
connected to the button cell)

3 button cells (3V)

light dependent resistor (LDR)

sheath for LDR

fibre optic cable.
Activity 2 Combining colours
What this activity illustrates: Different combinations of red, green and blue light can be used to create
any perceived colour. A combination of all three in the right proportion can create the appearance of
white light.
What you need from this pack: 3 LEDs (red, green and blue), 3 button cells (3V).
What to do
Take a button cell from the pack (keep the packaging for the button
cells to store them in after you have finished -- they should not be put
back in the bag loose or they may short-circuit). The base of the cell is
marked with a ‘+’.
Take one of the LEDs – notice that one leg is longer than the other.
Hold the LED with the legs either side of the cell as shown, with the
longer leg on the ‘+’ side. The LED should light up.
Get another LED and cell, and do the same thing. Point both LEDs at a piece of white paper so the
colours overlap. Try mixing the colours and varying their intensities by moving one LED away from or
closer to the paper.
Using the third LED, try other combinations of colours, including three LEDs together (you'll probably
find it easiest to do this using three hands!).
Explanation
The human eye has three different types of colour receptors (cone cells) which are sensitive to light in
the red, green and blue regions of the spectrum respectively (there is some overlap between them).
All the colours that we perceive therefore arise from different patterns of stimulation of these
receptors. So, because there are only three kinds of cones, in principle, it is possible just using three
LEDs (red, green and blue) to produce any perceived colour. For example, by simultaneously
stimulating both the ‘red’ and ‘green’ cones by using a red and a green LED, it is possible to produce a
© 2009 GATSBY SCIENCE ENHANCEMENT PROGRAMME
3
WAVES AND RADIATION SAMPLE PACK
perception of yellow. A computer monitor uses the same principle. There are three different kinds of
pixel on a computer monitor (red, green and blue), and different colours are produced by varying the
intensities of these.
Other things to do
Look at how custom colours can be produced in a computer word processor. This shows different
proportions of red, green and blue, give rise to different colours on the screen.
Activity 3 Signalling using fibre optics
What this activity illustrates: Radiation can be used to send signals. It is useful to think of this in terms
of a source and a detector, and the journey from source to detector. This activity shows the basic
principles of the use of fibre optic cable in communications.
What you need from this pack: light dependent resistor (LDR), sheath, fibre optic cable, LED, button
cell.
Other things you will need: digital multimeter, 2 plug-plug leads (one red, one black), 2 croc clips,
(optional: piece of black tape, scissors).
What to do
Push the LDR so that it is just inside the sheath with the legs coming out of the back, and put the
length of fibre-optic cable into the hole at the other end of the sheath (as shown below left). You may
find it helpful to cover the back with a small piece of black tape.) Connect the LDR to a digital
multimeter (as shown below right).
Turn the knob on the multimeter to a resistance scale – you need to find an appropriate scale that will
show a proper value. If the reading just displays ‘1’, then you need to turn the knob to a lower
resistance scale.
Point the exposed end of the fibre-optic cable at a light source, e.g. a desk lamp, or an LED connected
to a button cell. Notice what happens to the resistance reading. How could this be used as a signalling
system?
© 2009 GATSBY SCIENCE ENHANCEMENT PROGRAMME
4
WAVES AND RADIATION SAMPLE PACK
Explanation
This simple equipment illustrates the principle of a signalling system, with a source (LED), journey
(fibre optic cable) and detector (light dependent resistor). Signals can be sent as pulses of light, and
detected by the variation in the resistance of the light dependent resistor.
The principle of an optical fibre is that light can travel along its length even when it is curved, being
reflected by total internal reflection before emerging at the end of the fibre. In real applications, lasers
are able to convert electrical digital signals into very fast pulses of light, up to hundreds of millions of
times per second. The best-quality fibres currently available can sustain transmission distances of
around 100 km before amplification of the signal is needed. The advantages of optical fibres over
copper wire for carrying signals are that they are less expensive and can be made thinner with higher
carrying capacity.
BAG C: INFRARED RADIATION
The contents of this bag:

phototransistor (the end of this is dark)

infrared emitter diode (the end of this is
lighter than the phototransistor)

2 resistors (82Ω)

2 terminal blocks

2 battery boxes (each needs 2 AA cells
– not included).
Activity 4 Detecting infrared radiation
What this activity illustrates: Infrared (IR) radiation is
invisible to the naked eye, but it can be detected by a
device called a phototransistor. When exposed to IR
radiation, the electrical resistance of a phototransistor
decreases.
What you need from this pack: phototransistor.
Other things you will need: digital multimeter, 2 plug-plug
leads (one red, one black), 2 croc clips, access to a range
of sources that emit radiation, e.g. conventional
(incandescent) light bulb, fluorescent strip, radiant heater.
Connect the phototransistor to a multimeter, with the longer
leg connected to the black lead (negative). (Note that this is
different to an LED where the longer leg is always
connected to positive.)
© 2009 GATSBY SCIENCE ENHANCEMENT PROGRAMME
5
WAVES AND RADIATION SAMPLE PACK
Turn the knob on the multimeter to a resistance scale – you need to find an appropriate scale that will
show a proper value. If the reading just displays ‘1’, then you need to turn the knob to a lower
resistance scale.
Point the phototransistor at a range of sources of radiation, e.g. a conventional (incandescent) light
bulb, a radiant heater, and a fluorescent strip light. What happens to the resistance of the
phototransistor? Which of these sources emits most IR radiation?
Explanation
The resistance of a phototransistor drops dramatically when it is pointed at an incandescent light bulb;
the effect is much less marked with a fluorescent light. An incandescent lamp gives out a great
proportion of IR radiation, which is why it is much less energy efficient than a fluorescent lamp which
gives out relatively little IR. If a radiant heater is available, this is a good starting point for explanations
to pupils about IR radiation. It gives out relatively little light, but the warming effect of the radiation from
it can be felt easily by the body; it can be seen that the phototransistor detects this ‘invisible’ radiation.
Activity 5 Signalling with infrared radiation
What this activity illustrates: A TV remote control uses infrared (IR) radiation to send signals. A simple
IR signalling system that shows this principle can be made consisting of a transmitter (with an infrared
emitter diode) and a receiver (with a phototransistor as used in the previous activity).
This photograph shows what the transmitter and receiver look like when assembled. The transmitter
(left) has an infrared emitter diode connected to a battery box (it also includes a resistor). The receiver
(right) has a circuit containing a phototransistor and a red LED connected to a battery box; the red
LED lights up to show when IR radiation from the transmitter is detected.
A mobile phone camera is sensitive to IR radiation as well as to visible light, so it can be used to
demonstrate that the transmitter is emitting invisible IR radiation.
What you need from this pack: phototransistor, infrared emitter diode, 2 resistors (82Ω), 2 terminal
blocks, 2 battery boxes, red LED (from Bag B).
Other things you will need: 4 AA cells, small screwdriver, mobile phone camera (or similar, e.g.
webcam, digital camera).
N.B. A resistor is used in a circuit with an LED in order to limit the current passing through it and thus
avoid damage.
© 2009 GATSBY SCIENCE ENHANCEMENT PROGRAMME
6
WAVES AND RADIATION SAMPLE PACK
What to do
First, make up the infrared transmitter, by inserting the components as shown below into a terminal
block. It is essential that the components are connected the right way round or they will not work.
N.B. Make sure that the screws in the terminal
blocks make good electrical connections with the
legs on the components and on the metal wire at the
end of the leads from the battery box.
When you have assembled the transmitter, insert two AA cells and switch on. Infrared radiation is
invisible so nothing will appear to happen, but what do you see if you look at the IR emitter diode using
a mobile phone camera?
Once you have got the transmitter working, you are now ready to make the receiver. Insert the
components as shown below into a terminal block, and then put two cells in the battery box.
(If you wish, you can make this in two stages to test
as you go along. First, use a resistor (82Ω) instead
of the phototransistor, to check that the red LED
comes on when you switch on the battery box. Then
replace the resistor by a phototransistor.)
Point the IR transmitter at the phototransistor on the receiver; if the receiver is working, the red LED
will light up.
© 2009 GATSBY SCIENCE ENHANCEMENT PROGRAMME
7
WAVES AND RADIATION SAMPLE PACK
Explanation
When the transmitter is switched on and pointed at a mobile phone camera, the infrared emitter diode
should appear as bright white – the image sensor in the camera detects infrared as well as visible
radiation. When the transmitter is pointed at the receiver, the infrared radiation causes the resistance
of the phototransistor to drop, thus more current flows in the circuit, and the red LED lights up. By
switching the transmitter on and off, the red LED can be made to go on and off, and thus a signal can
be sent.
In Activity 3, the idea of thinking a signalling system in terms of source-journey-detector was
introduced. Here, the IR emitter diode is the source, and the phototransistor is the detector. The IR
radiation travels here through the air (the journey) though a medium is not needed – electromagnetic
radiation can travel through a vacuum.
Other things to do
See what happens if you change the ‘journey’ of the IR radiation. Does it pass through materials, for
example, glass, polythene, a black bin liner? Can it be reflected with a mirror? Try pointing a TV
remote control at the receiver – can you see the red LED on the receiver flashing?
BAG D: MICROWAVE AND ULTRAVIOLET RADIATION
The contents of this bag:

Phone Flasher

conductive fabric

ultraviolet LED

glow-in-the-dark film

4 ultraviolet sensitive beads.
Activity 6 Microwave radiation
What this activity illustrates: A mobile phone produces microwave radiation, and this radiation is able
to pass through some materials but not others.
What you need from this pack: Phone Flasher, conductive fabric, a wet paper towel.
Other things you will need: 2 mobile phones.
What to do
Carefully remove the plastic battery tab on the Phone Flasher before using it. Put the Phone Flasher
next to one of the mobile phones, and then call it from the other. Notice how the Phone Flasher
detects microwave radiation and starts to flash before the phone rings (this occurs because signals
are being sent to establish a connection before it is made, a process called ‘handshaking’). Wait for
© 2009 GATSBY SCIENCE ENHANCEMENT PROGRAMME
8
WAVES AND RADIATION SAMPLE PACK
the flashing to stop and repeat the experiment, but this time wrapping the Phone Flasher in conductive
fabric (this is a fabric whose threads are coated with metal). What is the effect of the fabric on
microwave radiation? Hold a wet paper towel between the phone and the Phone Flasher. Does the
wet towel let microwave radiation through it?
Explanation
Microwave radiation is reflected off metal objects and does not pass through them. Water absorbs
microwave radiation. This is the principle of the microwave oven – foods containing water absorb the
radiation and become hotter. The heating effects of microwave radiation from a mobile phone on any
water-containing objects are far too small though to be detectable with conventional thermometers.
Other things to do
Try putting other objects between the mobile and the Phone Flasher to see what absorbs microwave
radiation and what does not, for example, a book, a hand, a piece of wood, a cup of tea, an apple.
Activity 7 Ultraviolet radiation
What this activity illustrates: Ultraviolet (UV) radiation can be used to make certain materials
phosphoresce or fluoresce. Ultraviolet radiation is emitted by the Sun.
What you need from this pack: ultraviolet LED, button cell and coloured LEDs (from Bag B), glow-inthe-dark film, ultraviolet sensitive beads.
Other things you will need: fluorescent highlighter pens, sheet of paper.
What to do
Make the UV LED light up by holding its legs either side of a button cell (as in Activity 2). Point it at the
glow-in-the-dark film; using UV light, write your initials on the film. Repeat with red, green and blue
LEDs. How does the film respond to these different frequencies?
Draw on a sheet of paper with a few different fluorescent highlighter pens. In a darkened room, shine
the UV light from the LED on the paper. What do you see?
UV sensitive beads change colour when exposed to UV radiation. Put a UV sensitive bead just outside
a window, and another one just inside a window (this works best on a sunny day). What happens to
the beads? What is the effect of glass on ultraviolet radiation?
Explanation
Glow-in-the dark paper contains a phosphorescent material; when it is exposed to UV radiation, the
molecules absorb these high-energy photons and become excited (they are promoted to a higher
energy state). Then, over time, the molecules change back to their original lower energy state and
emit lower energy photons (this appears as green light). Blue light has photons of sufficiently high
energy to make the material phosphoresce; the photons in green light and red light are not of high
enough energy to do this. Highlighter pens contain fluorescent materials; fluorescence is similar to
phosphorescence, except that after excitation, the molecules emit radiation immediately. So,
fluorescent materials appear bright because they absorb higher energy radiation and emit it as visible
radiation, but they do not continue to emit radiation when the source is removed.
UV sensitive beads left outside a window will change colour faster than those inside; much of the UV
radiation from sunlight is absorbed by the glass in the window.
© 2009 GATSBY SCIENCE ENHANCEMENT PROGRAMME
9
WAVES AND RADIATION SAMPLE PACK
Other things to do
Real teeth fluoresce, though false teeth and crowns often do not (more recent high-quality dental
materials may fluoresce); pointing the UV LED at a set of teeth can reveal which are real teeth and
which are not. The UV LED can also be used to reveal the presence or absence of fluorescence in
other everyday materials such as paper, clothes or washing powders. (N.B. To reduce forgery,
banknotes have fluorescent markings on them, but they need a higher frequency UV radiation than
that from the UV LED to reveal them.)
BAG E: WAVE PROPERTIES OF RADIATION
The contents of this bag:


SEP diffraction grids
2 pieces of polarising film.
Activity 8 Diffraction
What this activity illustrates: The structure
of DNA gives rise to a characteristic X-ray
diffraction pattern. Crick and Watson
used the information they obtained from
Rosalind Franklin’s photograph of the
diffraction pattern to work out its doublehelix structure.
What you need from this pack: SEP diffraction grids.
Other things you will need: desk lamp, piece of cardboard with pinhole.
What to do
Put a sheet of cardboard with a
pinhole in front of a desk lamp.
Switch on the desk lamp, and
hold the diffraction grid about a
metre in front of it. Look through
the grid at the pinhole. What
pattern can you see when you
look through the horizontal lines?
Now repeat looking through the
zigzag lines. What pattern can
you see?
Explanation
The first grid produces a vertical series of dots of light; the second grid produces an X-shape pattern.
What Watson saw in Franklin’s photograph was an X-shaped series of markings, and the way in which
a helix can give rise to such a diffraction pattern is not difficult to understand.
© 2009 GATSBY SCIENCE ENHANCEMENT PROGRAMME
10
WAVES AND RADIATION SAMPLE PACK
A horizontal set of lines will produce a diffraction pattern consisting of a vertical series of dots: the
closer the spacing of the lines the wider separation of the dots. A helix, when viewed from the side,
appears as a set of zigzag lines, that is, two sets of parallel lines at different orientations. The ‘zigs’
produce a set of dots in one orientation, and the ‘zags’ produce a set in another orientation, hence the
X-shape of the pattern. The spacing of the lines on these diffraction grids are around 0.1 mm, and they
diffract light in the visible region. To obtain diffraction patterns of the much smaller dimensions in DNA,
radiation of a shorter wavelength is needed; the use of X-rays with DNA produced diffraction patterns
from which it was possible to calculate the critical dimensions needed to elucidate its structure.
Activity 9 Polarisation
What this activity illustrates: Light waves oscillate in different orientations.
What you need from this pack: 2 pieces of polarising film.
Other things you will need: small bowl of water, computer monitor.
What to do
Put a bowl full of water on a table and stand so that you can see a source of light (e.g. a window)
reflected off the surface. Look at the surface of the water though one of the polarising films and rotate
the film. What do you notice about the reflection? Now look at the source of light itself through the film,
and rotate it. What do you see?
Explanation
The light waves given off by the Sun or by a light bulb oscillate in all directions. However, when light
reflects off water, waves that are oscillating in a vertical direction tend to enter the water, while those
oscillating in a horizontal direction tend to be reflected. Radiation which shows a particular orientation
is said to be polarised. Polarising film tends to let through light that is oscillating in one direction, and
tends to block that which is oscillating at right angles to this. So, in one orientation of the polarising
film, the light from the water passes through, but if it is turned 90° the light from the water is blocked.
Polarising film is used in some sunglasses to reduce glare from the water.
What to do
Place one piece of polarising film on top of the other and look through them. Rotate one of them and
observe what happens. Put one piece of the film in front of a computer monitor and observe what
happens when you rotate the film.
Explanation
When the two pieces of film are lined up, light can pass through; when they are right-angles to each
other (cross-polarised), the light is blocked. The light from a computer screen is polarised (at 45°).
Holding the film at 45°, then rotating by 90°, shows that one orientation will let the light through while
another blocks it.
Other things to do
Try looking at other LCD displays (different devices have different orientations of polarisation – this
can cause problems when wearing polarised sunglasses, for example, if driving and reading a car
display). After rain, try looking at the differences between wet and dry surfaces outside. Put a CD case
in front of a computer monitor and then observe through a piece of polarising film to see the stress
patterns in the plastic case.
© 2009 GATSBY SCIENCE ENHANCEMENT PROGRAMME
11
WAVES AND RADIATION SAMPLE PACK
FURTHER INFORMATION
Curriculum materials
The Gatsby Science Enhancement Programme
(www.sep.org.uk) publishes the Innovations in Practical
Work series of publications. The following booklets in
this series have further ideas and suggestions for
teaching about the electromagnetic spectrum:



Radiation and communication
Seeing beyond the visible
Light and matter: models and applications.
For more information about the science behind these
activities, visit www.sep.org.uk/wavespack which gives
links to useful websites.
Gatsby Science Enhancement Programme
Middlesex University
S37 Stable Yard
Bramley Road
London N14 4YZ
Email:[email protected]
Web: www.sep.org.uk
To keep up-to-date about the work of SEP and to obtain
free copies of its new publications, sign up as an SEP
Associate by visiting the SEP website.
Practical resources
SEP works in close collaboration with Middlesex
University Teaching Resources (MUTR) in developing
new practical resources. The materials in this pack can
be purchased from MUTR. Visit www.mutr.co.uk for
further details.
Teaching Resources
Middlesex University
Unit 10, The IO Centre
Lea Road, Waltham Cross
Hertfordshire EN9 1AS
Tel: 01992 716052
Fax: 01992 719474
Email: [email protected]
Web: www.mutr.co.uk
© 2009 GATSBY SCIENCE ENHANCEMENT PROGRAMME
12