P3 1.1a – Student worksheet
EM spectrum revision
The cards below show the names of the different parts of the electromagnetic spectrum, and some
of the properties of the waves. The wavelengths given are approximate. Cut out the cards and
match them up. (7 marks)
Radio waves
 = 1 m to 3 x 103 m
Used for transmitting TV
programmes
 = 10-11 m to 10-10 m
Visible light
X-rays
Detected by eyes and
cameras.
Used for transmitting phone
calls and for cooking.
 = 10-3 m to 1 m
Detected by photographic films
and special cameras. Can go
through some materials. Can
cause cancer.
Gamma rays
Detected by photographic films
and special cameras. Can go
through some materials. Can
cause cancer.
 = 4 x 10-7 m to 10-3 m
Infrared
 = 7 x 10-7 m to 4 x 10-7 m
Microwaves
 = 10-10 m to 10-9 m
Ultraviolet
Detected by skin, used for
communication in optical fibres
Causes suntans and may
cause skin cancer.
 = 10-9 m to 7 x 10-7 m
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P3 1.1c – Student worksheet
X-ray questions
1
The names below are parts of the electromagnetic spectrum. Write them in order, starting with
the waves with the longest wavelengths. (1 mark)
gamma rays, infrared, microwaves, radio waves, ultraviolet, visible light, X-rays
2
3
a
Which of the types of radiation listed in question 1 are ionising radiations? (2 marks)
b
Explain why these are the only types that cause ionisation. (1 mark)
c
What happens when X-ray radiation ionises a molecule? (2 marks)
d
Describe some of the effects that ionisation can have on the body. (2 marks)
Radiation can be transmitted by a material, partially or completely reflected or absorbed.
a
What happens to light when it hits the following materials? (5 marks)
i
glass
ii
skin
iii bone
iv metal
v
plastic
b
What happens to X-rays when they hit the materials listed above? (5 marks)
c
Explain why the differences in your answers to parts a and b make X-rays useful. (1 mark)
4
Describe two ways in which X-rays can be detected to form an image. (2 marks)
5
Explain why more X-rays are needed to make a CT-scan than to make a simple X-ray image.
(1 mark)
Extension
6
Explain why a material that reflects X-rays will look the same as a material that absorbs them
on an X-ray image. (2 marks)
7
Explain why a material that reflects light will look different to a material that absorbs light on a
normal photograph. (2 marks)
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P3 1.2a – Student worksheet
Representing waves
The diagrams below represent oscilloscope traces of different sound waves.
1
Sound waves are longitudinal waves. Explain how the transverse waves shown below can
represent sound waves. (1 mark)
2
Copy one wave and mark on it the amplitude and wavelength. (2 marks)
3
Write down the letters for pairs of cards that have the same loudness. (2 marks)
4
Write down the letters for pairs of cards that have the same pitch. (2 marks)
5
Which sounds have a higher pitch than the one shown on card A? (2 marks)
6
Which sounds have a lower pitch than the one shown on card L? (2 marks)
7
Which sounds are louder and lower than the one shown on card L? (1 mark)
8
Which sounds are quieter and lower than the one shown on card L? (1 mark)
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P3 1.2c – Student practical sheet
Modelling ultrasound reflections
Echoes from sound waves hitting an object can be used to model ultrasound reflections and to
determine the distance from the sound source to the object.
Aim
To use echoes to measure the distance to an object.
Equipment
●
a clapperboard or two pieces of wood or
several balloons
●
datalogger to record sound pulses from the
microphone
●
microphone
●
measuring tape
●
optional: hygrometer
●
optional: thermometer
Safety
●
Take care to keep fingers out of the way when banging the clapperboard or wood together.
What you need to do
1
You are going to make a sudden sound by banging a clapperboard or two pieces of wood
together, or by bursting a balloon. By recording the time it takes for you to hear an echo of the
sound, you can work out the distance to the object from which the sound has reflected.
2
Choose an object to measure a distance to, such as a wall or the side of a building. Choose a
measuring position at a distance from the object and use the measuring tape to find the
distance between the measuring position and the object.
3
Your teacher will help you to set up the datalogging equipment to detect the bang that you
make and the echo.
4
Record the time between a bang and the echo several times, and record your results.
5
If you have time, make another set of measurements from a different distance, or to a different
object.
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P3 1.2c – Student practical sheet
Using the evidence
1
Present your times in a table, including a mean of the results for each object or distance.
(2 marks)
2
Use the formula s = v x t to calculate the distance to the object for each object or distance.
Use 340 m/s for the speed of sound in air. (2 marks)
Evaluation
3
How repeatable were your measurements of the echo time? Explain your answer. (2 marks)
4
How close was your calculated distance to the distance found using the measuring tape?
Express the difference as a percentage of the measured distance. (2 marks)
5
Suggest some reasons for any difference between the calculated and measured distances.
(2 marks)
6
Explain how you could reduce the effects of the sources of error you have described in
question 5. (2 marks)
7
List the differences between your system and an ultrasound system used in medical scanning.
(3 marks)
Extension
8
The value of 340 m/s is an average. The speed of sound in air depends on the air temperature
and the relative humidity, and also to a lesser extent on the air pressure.
a
Record the relative humidity and temperature. (2 marks)
b
Find out and explain what relative humidity means. (2 marks)
c
Use the speed of sound calculator on the NPL Acoustics webpage to work out a more
accurate value for the speed of sound for the place and time you carried out your
measurements. (1 mark)
d
How has using this value changed the error in your results? (3 marks)
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P3 1.2d – Student worksheet
Ultrasound questions
The table shows the speed of sound in different materials.
Material
Speed of sound (m/s)
fat
1450
liver
1575
muscle
1600
1
Describe the similarities and differences between sound and ultrasound. (2 marks)
2
The distance travelled by a sound can be calculated from the time the sound takes to be
detected after reflecting off a boundary. Why does this distance need to be divided by 2?
(1 mark)
3
If two pieces of body tissue of equal thickness were measured using ultrasound, why might the
time taken for the reflection be different for each piece? (1 mark)
4
An ultrasound machine sends a pulse of ultrasound into a layer of fat and detects an echo
30 s later. 1 s = 1 microsecond = 1 x 10-6 s.
a
How far has the ultrasound pulse travelled? (3 marks)
b
How thick is the layer of fat? (3 marks)
5
If the machine in question 4 had been measuring a layer of muscle instead, what would the
thickness of the muscle be? (4 marks)
6
Ultrasound machines used in medicine are set up to use a standard speed of 1540 m/s.
a
What thickness would this machine have worked out for the measurement described in
question 4? (4 marks)
b
What would be the error in this thickness if the tissue measured was liver tissue? (6 marks)
Extension
7
The speed of sound in muscle actually varies between 1540 and 1630 m/s. A standard
machine is used to measure the thickness of muscle tissue.
a
Will the measurement be larger or smaller than the real thickness? Explain your answer.
(3 marks)
b
Express the maximum error as a percentage, for a muscle thickness of 1.5 cm. (6 marks)
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P3 1.2e – Student worksheet
Ultrasound in industry
A manufacturing company uses ultrasound to check that the polythene sheets they make are the
correct thickness. Figure 1 shows the machine used to do this. The speed of sound in polythene is
0.27 centimetres per microsecond (cm/µs). If the sheet is the correct thickness, the ultrasound
detector receives an echo after 3.6 µs.
Figure 1
1
Explain how the machine detects the thickness of the polythene. (3 marks)
2
How thick is the sheet supposed to be? (2 marks)
3
The machine receives an echo after 3.8 µs.
4
a
Is the polythene sheet too thick or too thin? Explain your answer. (2 marks)
b
By how much is it too thick or thin? (3 marks)
The machine is adjusted to check the thickness of a thinner sheet. Should the detector receive
the echo in a shorter or longer time than 3.6 µs? Explain your answer. (2 marks)
The same machine can be used to detect the thickness of steel plates. The machine receives an
echo after 2.2 µs if the steel is the correct thickness. The speed of sound in steel is 0.63 cm/µs.
5
How thick should the steel be? (2 marks)
6
During one test, the machine receives a faint echo after only 0.5 µs as well as a strong echo at
2.2 µs. Suggest what could have caused the faint echo, and where it is. (3 marks)
The object in Figure 2 is to be scanned using ultrasound. There is a fault in the metal and this is
what the scan is looking for.
Figure 2
The metal block is drawn life size.
The speed of sound in this block is
5000 m/s.
Extension
7
Draw a set of oscilloscope traces for the ultrasound scan that the operator might see when the
scanner is positioned at a, b, c and d. Show your working. (6 marks)
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P3 1.3a – Student worksheet
Ultrasound scans
Some ultrasound is reflected each time an
ultrasound wave passes from one medium to
another. The proportion reflected depends on how
different the speed of sound is between the two
materials, and on the difference between their
densities. Water, skin and muscle all have similar
(but not identical) properties. The table shows
some typical values.
Sound travelling
% reflected
from
to
air
skin
99%
air
water
99%
water
skin
0.1%
skin
muscle
0.1%
The diagrams in Figure 1 show two ultrasound scans being made. The scanner both sends and
detects ultrasound as it is moved over the woman's abdomen.
Figure 1
This flowchart (Figure 2) shows what is happening in diagram X.
Figure 2
1
Copy and complete this flow chart (Figure 3) to show what is happening in diagram Y. (1 mark)
Figure 3
2
3
a
How much of the ultrasound will be reflected between stages B and C? (1 mark)
b
How much of the ultrasound will be left to reflect of the foetus inside the woman's body?
(1 mark)
c
The jelly used in diagram Y is similar to water. How much of the ultrasound will be reflected
between stages F and G? (1 mark)
d
How much of the ultrasound will be left to reflect off the foetus inside the woman's body?
(1 mark)
e
Explain in your own words why jelly is used in ultrasound scans, and why the scanner must
be touching the jelly. (3 marks)
The distance between the mother's skin and the back of the foetus' head is about 15 cm. The
speed of sound in muscle is approximately 1580 m/s. How long will it take an ultrasound wave
to travel this distance and back again? (3 marks)
Extension
4
Explain why the time you have calculated is not likely to be the correct value. (2 marks)
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P3 1.4a – Student worksheet
Ultrasound and X-rays
1
2
In what ways are sound and ultrasound:
a
similar (2 marks)
b
different? (2 marks)
List the key differences between the properties of ultrasound and X-rays. Include:
●
the type of wave and what they can travel through (3 marks)
●
their ionising ability (1 mark)
●
the materials they can penetrate (2 marks)
3
Why are X-rays and not ultrasound waves used to treat cancer? (2 marks)
4
Why are ultrasound waves and not X-rays used for:
a
pre-natal scans (2 marks)
b
breaking up kidney stones? (2 marks)
5
What is a CT scan? (2 marks)
6
a
Why is the risk of harm to the patient higher if they have a CT scan compared to having an
X-ray image made of a broken bone? (2 marks)
b
Given that the risk to the patient is higher for a CT scan than for a normal X-ray, why are
CT scans used? (2 marks)
7
8
What precautions are taken by radiographers using X-rays to:
a
protect themselves from harmful effects of radiation (3 marks)
b
protect their patients? (1 mark)
Explain how the precautions you listed in your answer to question 7 help to reduce the risk of
harm from X-rays. (3 marks)
Extension
9
Some airport body 'backscatter' scanners expose travellers to small doses of X-ray radiation.
Find out how much this dose is compared to the radiation received on a typical transatlantic
flight. Do you think the potential risk to passengers from using these body scanners is justified?
(4 marks)
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