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GCSE · Physics

P6b The Electromagnetic Spectrum

AQA 8464 · Calculator allowed · about 80 minutes

Total Marks

Name: _______________________________ Date: ____ / ____ / ______

Answer ALL questions. Show all your working.

Key words and equations: The electromagnetic spectrum (P6b)

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All electromagnetic (EM) waves are transverse waves that transfer energy from a source to an absorber, and they can all travel through a vacuum at the same speed, the speed of light, 3.0 x 10^8 m/s. The electromagnetic spectrum is a continuous range of these waves, grouped by wavelength and frequency. In order of increasing wavelength (decreasing frequency), the seven groups are: gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves, radio waves. Different parts of the spectrum are generated and detected in different ways, have different everyday uses, and have different effects on living cells. Higher-frequency waves, such as X-rays and gamma rays, carry more energy and are ionising, meaning they can remove electrons from atoms and molecules; this can damage or mutate the DNA in living cells, causing harm. When an electromagnetic wave crosses a boundary between two different materials, it can change speed and wavelength, and refract (change direction), although its frequency stays the same. Equation used in this worksheet: wave speed = frequency * wavelength (v = f * lambda), where v = 3.0 x 10^8 m/s for all electromagnetic waves in a vacuum (or air). Every equation needed is given within the question itself - you do not need to memorise it for this worksheet.

The list below shows the seven types of electromagnetic wave in order of increasing wavelength, but three of the labels are missing. State the correct type of wave for each gap.
Gamma rays, X-rays, (i) ______, Visible light, (ii) ______, Microwaves, (iii) ______

(Total for Question 1 is 3 marks)

State one everyday use of each of the following types of electromagnetic wave.
(i) Microwaves
(ii) Infrared
(iii) Ultraviolet
(iv) Gamma rays

(Total for Question 2 is 4 marks)

Radio waves are used to broadcast television and radio programmes. Describe how radio waves used for broadcasting are generated, and how they are then detected by a receiver aerial.

(Total for Question 3 is 2 marks)

Describe two ways that exposure to ultraviolet radiation can harm the human body.

(Total for Question 4 is 2 marks)

High-power microwave radiation can be dangerous to the human body. Describe how excessive exposure to microwaves can harm human tissue.

(Total for Question 5 is 2 marks)

State two precautions a hospital radiographer can take to reduce their own exposure to X-rays while working.

(Total for Question 6 is 2 marks)

X-rays and γ rays are examples of ionising radiation. Radio waves and microwaves are not ionising.

(a)Explain why ionising radiation, such as X-rays and γ rays, can be more hazardous to the human body than non-ionising radiation, such as radio waves.(2)

(b)State one factor, other than the type of radiation, that affects the size of the radiation dose a person receives from a source of ionising radiation.(1)

(Total for Question 7 is 3 marks)

A microwave oven produces microwaves with a wavelength of 12 cm. Use the Physics Equations Sheet: wave speed = frequency * wavelength (v = f * λ), and the speed of electromagnetic waves in air, v = 3.0 x 10⁸ m/s, to calculate the frequency of these microwaves.

(Total for Question 8 is 3 marks)

A local radio station broadcasts on a frequency of 97.4 MHz. Use the Physics Equations Sheet: wave speed = frequency * wavelength (v = f * λ), and the speed of electromagnetic waves in air, v = 3.0 x 10⁸ m/s, to calculate the wavelength of the radio waves broadcast. Give your answer to 3 significant figures.

(Total for Question 9 is 3 marks)

A hospital X-ray machine produces X-rays with a wavelength of 5.0 x 10^-11 m. Use the Physics Equations Sheet: wave speed = frequency * wavelength (v = f * λ), and the speed of electromagnetic waves in air, v = 3.0 x 10⁸ m/s, to calculate the frequency of these X-rays.

(Total for Question 10 is 3 marks)

X-rays and γ rays are both highly energetic electromagnetic waves, but they are produced in different ways.

(a)Describe how X-rays are produced.(2)

(b)Describe how γ rays are produced.(1)

(Total for Question 11 is 3 marks)

A ray of visible light travels from air into a glass block, hitting the boundary at an angle to the normal (not along the normal). Describe what happens to the light ray's speed, wavelength, frequency and direction as it crosses the boundary from air into the (optically denser) glass.

(Total for Question 12 is 4 marks)

Required practical: A student wants to compare how much infrared radiation is emitted by different surfaces, all at the same temperature. They have a Leslie cube (a hollow metal cube with four different surface finishes on its sides: matte black, matte white, shiny black and shiny silver) that can be filled with hot water, and an infrared detector.

(a)Describe how the student could use this apparatus to carry out a fair test comparing the infrared radiation emitted by the four surfaces.(3)

(b)State which surface would be expected to emit the most infrared radiation, and which would be expected to emit the least.(2)

(Total for Question 13 is 5 marks)

Required practical: Two identical metal drinks cans are prepared, one painted matte black and one polished to a shiny silver finish. Both cans are filled with 100 cm3 of water at the same starting temperature and placed the same distance from an infrared heater. Each can's water temperature is measured before and after 5.0 minutes of heating.
Matte black can: temperature rises from 18.0 degrees C to 33.5 degrees C.
Shiny silver can: temperature rises from 18.0 degrees C to 22.0 degrees C.

(a)Calculate the mean rate of temperature increase, in degrees C per minute, for the matte black can.(2)

(b)Calculate the mean rate of temperature increase, in degrees C per minute, for the shiny silver can.(2)

(c)Use your answers to parts a and b to write a conclusion about how surface finish affects the absorption of infrared radiation.(1)

(Total for Question 14 is 5 marks)

A student repeats the matte black can experiment from question 14 three times, each time heating for 5.0 minutes from a starting temperature of 18.0 degrees C. The final temperatures recorded were 33.5 degrees C, 33.0 degrees C and 38.5 degrees C.

(a)Identify which of the three results is anomalous.(1)

(b)Suggest one possible reason for this anomalous result.(1)

(c)Calculate the mean final temperature using only the two valid (non-anomalous) results.(2)

(Total for Question 15 is 4 marks)

Visible light has wavelengths that range from about 400 nm (violet light) to about 700 nm (red light). Use the Physics Equations Sheet: wave speed = frequency * wavelength (v = f * λ), and the speed of electromagnetic waves in air, v = 3.00 x 10⁸ m/s, to calculate the maximum frequency found in the visible light range.

(Total for Question 16 is 4 marks)

A γ-ray source used in radiotherapy emits electromagnetic radiation with a frequency of 3.00 x 10¹⁹ Hz.

(a)Use the Physics Equations Sheet: wave speed = frequency * wavelength (v = f * λ), and the speed of electromagnetic waves, v = 3.00 x 10⁸ m/s, to calculate the wavelength of this γ radiation. Give your answer in standard form.(3)

(b)Radiotherapy uses γ rays, rather than radio waves, to destroy cancer cells deep inside the body. Explain why γ rays, rather than radio waves, are suitable for this use.(2)

(Total for Question 17 is 5 marks)

Higher tier only. Some electromagnetic waves, such as infrared, visible light and ultraviolet, are absorbed and emitted because of changes in the energy levels of electrons within atoms. Explain, using ideas about electron energy levels, how an atom can absorb electromagnetic radiation and then later emit electromagnetic radiation.

(Total for Question 18 is 3 marks)

Higher tier only. Both γ rays and infrared radiation are electromagnetic waves, but γ radiation is far more hazardous to living cells than infrared radiation. Explain, in terms of frequency and ionisation, why this is the case.

(Total for Question 19 is 3 marks)

The electromagnetic spectrum has many uses in medicine, communication and everyday life, but different types of wave also present different dangers. Discuss the uses and dangers of ultraviolet radiation and γ radiation, and explain how these dangers are managed to keep people safe.

(Total for Question 20 is 6 marks)

Mark scheme · P6b The Electromagnetic Spectrum

Question 1

B1 (i) Ultraviolet
B1 (ii) Infrared
B1 (iii) Radio waves
Answer: (i) Ultraviolet (ii) Infrared (iii) Radio waves

Question 2

B1 (i) any suitable use, e.g. satellite communications, or cooking food (heating water molecules), oe
B1 (ii) any suitable use, e.g. electrical heaters, cooking, infrared cameras/thermal imaging, or remote controls, oe
B1 (iii) any suitable use, e.g. sun tanning/sunbeds, fluorescent lamps, or detecting forged bank notes/security marking, oe
B1 (iv) any suitable use, e.g. sterilising medical equipment, treating cancer (radiotherapy), or medical tracers, oe
Answer: (i) Satellite communications (ii) Electrical heaters/cooking (iii) Sun tanning (iv) Sterilising medical equipment / treating cancer.

Question 3

B1 generated by oscillations in an electrical circuit, oe
B1 detected because the radio waves induce oscillations (an alternating current) in the electrical circuit of the receiver aerial, oe
Answer: Generated by oscillations in an electrical circuit; detected because they induce oscillations (an alternating current) in the receiver aerial's circuit.

Question 4

B1 skin damage, e.g. premature ageing of the skin, or an increased risk of skin cancer, oe
B1 eye damage, e.g. damage to the eyes/increased risk of cataracts, oe
Answer: Skin damage (e.g. premature ageing or an increased risk of skin cancer) and eye damage (e.g. cataracts).

Question 5

B1 microwaves are absorbed by water molecules in the body's cells, oe
B1 this transfers energy to the tissue, causing internal heating, which can burn or damage living cells, oe
Answer: Microwaves are absorbed by water molecules in cells, transferring energy and causing internal heating that can damage tissue.

Question 6

B1 any one of: stand behind a lead/protective screen, or leave the room, during the scan; wear a lead apron, oe
B1 any other one of: wear a film badge/dosimeter to monitor the dose received; maximise distance from the source; minimise the time spent near the source, oe
Answer: E.g. stand behind a lead screen (or leave the room) during the scan, and wear a dosimeter badge to monitor their exposure.

Question 7

(a) B1 ionising radiation has enough energy to remove electrons from atoms or molecules (ionisation), oe
(a) B1 this can damage or mutate the DNA in living cells, which may lead to cell damage or cancer, oe
(a) Answer: Ionising radiation can remove electrons from atoms/molecules, which can damage or mutate DNA in cells, potentially causing cancer.
(b) B1 any one of: the distance from the source; the length/duration of exposure; the intensity/activity of the source; whether any shielding is used, oe
(b) Answer: E.g. the distance from the source (or the duration of exposure, or the activity of the source, or the shielding used).

Question 8

M1 converts 12 cm to 0.12 m
M1 rearranges and substitutes correctly: f = v/λ = (3.0 x 10⁸)/0.12
A1 f = 2.5 x 10⁹ Hz (2.5 GHz), cao
Answer: 2.5 x 10⁹ Hz (2.5 GHz)

Question 9

M1 converts 97.4 MHz to 9.74 x 10⁷ Hz
M1 rearranges and substitutes correctly: λ = v/f = (3.0 x 10⁸)/(9.74 x 10⁷)
A1 λ = 3.08 m (3 s.f.), cao (accept awrt 3.1 m)
Answer: 3.08 m

Question 10

M1 rearranges correctly: f = v/λ
M1 substitutes correctly: f = (3.0 x 10⁸)/(5.0 x 10^-11)
A1 f = 6.0 x 10¹⁸ Hz, cao
Answer: 6.0 x 10¹⁸ Hz

Question 11

(a) B1 electrons are accelerated to high speed and collide with a hard metal target, oe
(a) B1 the electrons decelerate rapidly on collision, and the energy lost is converted into (released as) X-ray radiation, oe
(a) Answer: High-speed electrons collide with a metal target and decelerate rapidly, releasing the energy lost as X-rays.
(b) B1 γ rays are emitted from the nucleus of a radioactive (unstable) atom, as it becomes more stable during radioactive decay, oe
(b) Answer: Emitted from the nucleus of a radioactive atom as it becomes more stable during decay.

Question 12

B1 speed decreases (the light slows down entering the denser glass), oe
B1 wavelength decreases, oe
B1 frequency stays the same (unchanged), oe
B1 the ray changes direction (refracts), bending towards the normal, oe
Answer: Speed decreases, wavelength decreases, frequency is unchanged, and the ray bends towards the normal.

Question 13

(a) B1 fill the Leslie cube with hot water (at a set/measured starting temperature, using a thermometer) so all four faces are at the same temperature, oe
(a) B1 hold/place the infrared detector at the same fixed distance from each face in turn, and record the detector reading for each surface, oe
(a) B1 control other variables (e.g. keep the water temperature, detector distance and time the same for each surface), and repeat each reading to check for reliability, oe
(a) Answer: Fill the cube with hot water at a set temperature, hold the detector the same fixed distance from each face in turn, controlling other variables and repeating for reliability.
(b) B1 the matte/dull black surface emits the most infrared radiation
(b) B1 the shiny silver surface emits the least infrared radiation
(b) Answer: Matte black emits the most; shiny silver emits the least.

Question 14

(a) M1 temperature rise = 33.5 - 18.0 = 15.5 degrees C, then divides by 5.0 minutes
(a) A1 3.1 degrees C per minute, cao
(a) Answer: 3.1 degrees C/min
(b) M1 temperature rise = 22.0 - 18.0 = 4.0 degrees C, then divides by 5.0 minutes
(b) A1 0.8 degrees C per minute, cao
(b) Answer: 0.8 degrees C/min
(c) B1 the matte black surface absorbed infrared radiation faster/more effectively than the shiny silver surface (which reflects more infrared radiation), ft from their (a) and (b) if black rate > silver rate shown, oe
(c) Answer: The matte black surface absorbs infrared radiation faster (its temperature rate is about four times higher), while the shiny silver surface reflects more of it.

Question 15

(a) B1 38.5 degrees C
(a) Answer: 38.5 degrees C
(b) B1 any sensible reason, e.g. the can may not have been kept the same distance from the heater for that trial, the thermometer reading may have been taken late or misread, or a draught/other heat source affected that trial, oe
(b) Answer: E.g. the can may have been closer to the heater for that trial, or the thermometer reading was taken late/misread.
(c) M1 (33.5 + 33.0) / 2, oe
(c) A1 33.25 degrees C (accept 33.3 degrees C), cao, ft from their identified anomaly in (a)
(c) Answer: 33.25 degrees C (33.3 degrees C to 3 s.f.)

Question 16

B1 identifies that the maximum frequency corresponds to the minimum (shortest) wavelength, 400 nm, since frequency and wavelength are inversely proportional (for fixed v), oe
M1 converts 400 nm to 4.00 x 10^-7 m
M1 rearranges and substitutes correctly: f = v/λ = (3.00 x 10⁸)/(4.00 x 10^-7)
A1 f = 7.5 x 10¹⁴ Hz, cao
Answer: 7.5 x 10¹⁴ Hz

Question 17

(a) M1 rearranges correctly: λ = v/f
(a) M1 substitutes correctly: λ = (3.00 x 10⁸)/(3.00 x 10¹⁹)
(a) A1 λ = 1.00 x 10^-11 m, cao
(a) Answer: 1.00 x 10^-11 m
(b) B1 γ rays are highly penetrating and ionising, so they can reach and damage cells deep inside the body, whereas radio waves are non-ionising and carry far less energy, so would not damage/kill the cells, oe
(b) B1 γ rays can be focused/directed at the tumour so that enough energy is transferred to damage the DNA of the cancer cells (killing them), oe
(b) Answer: Gamma rays are penetrating and ionising, so they can reach and damage cancer cells deep inside the body; they can be focused at the tumour to destroy its cells, unlike low-energy, non-ionising radio waves.

Question 18

B1 when an atom absorbs electromagnetic radiation of a specific frequency, an electron gains energy and moves to a higher energy level (further from the nucleus), oe
B1 the atom becomes excited/unstable, and the electron later falls back down to a lower energy level, oe
B1 this releases the energy as electromagnetic radiation of a specific frequency, equal to the energy difference between the levels, oe
Answer: The atom absorbs radiation of a specific frequency when an electron moves to a higher energy level; the electron later falls back down, emitting radiation of a specific frequency equal to the energy gap.

Question 19

B1 γ rays have a much higher frequency (and therefore carry much more energy) than infrared waves, oe
B1 γ rays are ionising: they can remove electrons from atoms/molecules in living cells, which can damage or mutate DNA and potentially cause cancer, oe
B1 infrared radiation is non-ionising and carries far less energy, so it mainly causes heating of tissue rather than ionisation/DNA damage, oe
Answer: Gamma rays have a much higher frequency and carry far more energy than infrared, making them ionising and able to damage cell DNA; infrared is non-ionising and mostly just causes heating.

Question 20

Level 1 (1-2): Simple, isolated statements are made about the uses and/or dangers of ultraviolet and/or gamma radiation, with limited or no reference to how the dangers are managed. The answer lacks a logical structure.
Level 2 (3-4): The uses and dangers of both ultraviolet and gamma radiation are described, with some reference to how the dangers are managed to keep people safe. There is some logical structure to the answer, but coverage of one wave type may be more complete than the other.
Level 3 (5-6): A detailed and logically structured discussion of the uses and dangers of both ultraviolet and gamma radiation is given, with a clear explanation of how each danger is managed to keep people safe. Points are linked using scientific reasoning throughout, for example comparing the relative frequency/energy of the two types of wave.
Indicative content:
- Ultraviolet uses: sun tanning/sunbeds, fluorescent lamps/energy-efficient lighting, security marking (e.g. pens that show up under UV light, or detecting forged bank notes).
- Ultraviolet dangers: causes premature ageing of the skin, increases the risk of skin cancer, and can damage the eyes (e.g. cataracts).
- Ultraviolet safety: using sunscreen/sun cream, wearing UV-protective clothing or sunglasses, limiting time spent in strong sunlight, and using shade.
- Gamma ray uses: sterilising medical/surgical equipment, treating cancer (radiotherapy), and medical tracers for diagnosis/imaging.
- Gamma ray dangers: gamma radiation is ionising, so it can damage or mutate DNA in living cells, increasing the risk of cancer, and can kill cells at high doses.
- Gamma ray safety: using lead shielding/lead-lined rooms, keeping distance from the source, limiting exposure time, and wearing a dosimeter badge to monitor the dose received by workers.
- Comparative/linking point: gamma rays have a much higher frequency (shorter wavelength) than ultraviolet, so gamma rays are more ionising and more penetrating, making them more hazardous overall and requiring stricter safety precautions, such as shielding and distance, rather than sunscreen alone.

The Electromagnetic Spectrum - Worksheets, Questions and Revision