Practise Properties of electromagnetic waves 2. 13 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
How electromagnetic waves are produced and absorbed (by changes in atoms and nuclei, and, at Higher tier, by oscillating currents in circuits), and the harm that ultraviolet, X-rays and gamma rays can do to the body. Expect recall questions and 'use the data' questions on radiation dose.
Grade by grade
What you need to be able to do, from the first marks up to the top grade.
3
Name the EM waves that harm body tissueUltraviolet, X-rays and gamma rays can have hazardous effects on human body tissue.
4
State the effects of ultraviolet on skinUltraviolet can make skin age prematurely and increases the risk of skin cancer.
5
State the effects of X-rays and gamma raysThey are ionising radiation and can cause mutation of genes and cancer.
5
State where gamma rays come fromGamma rays come from changes in the nucleus of an atom.
6
Use radiation dose data to compare risksCompare doses in sieverts or millisieverts: the bigger the dose, the greater the risk of harm.
7
Explain how radio waves are produced (HT)Oscillations (an alternating current) in an electrical circuit produce radio waves of the same frequency.
8
Explain how radio waves are received (HT)Radio waves absorbed by an aerial can induce an alternating current with the same frequency as the waves.
Notes
Producing and absorbing EM waves
EM waves over a wide range of frequencies can be produced or absorbed by changes inside atoms and their nuclei. For example, when electrons in atoms change energy level, EM waves such as light can be emitted or absorbed.
Gamma rays come from changes in the nucleus of an atom.
Radio waves and circuits (Higher tier only) grade 7+
Radio waves can be produced by oscillations in electrical circuits: an alternating current in a transmitter's aerial produces radio waves with the same frequency as the current.
When radio waves are absorbed by a receiver's aerial, they may create an alternating current with the same frequency as the radio waves. So radio waves can themselves induce oscillations in a circuit.
This is how a signal travels from a radio transmitter to a radio receiver.
Hazards to the body
Ultraviolet, 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.
Ultraviolet can cause skin to age prematurely and increases the risk of skin cancer.
X-rays and gamma rays are ionising radiation. They can cause the mutation of genes and cancer.
Radiation dose
Radiation dose, in sieverts (Sv), is a measure of the risk of harm from the body being exposed to radiation.
1000 millisieverts (mSv) = 1 sievert (Sv). You do not need to remember the unit, but you must be able to use it.
The bigger the dose, the greater the risk. Use given data to compare risks, for example the dose from a medical scan with the yearly dose from background radiation, and to judge whether a benefit is worth the risk.
Cheatsheet
EM waves can be produced or absorbed by changes in atoms and nuclei
Gamma rays come from changes in the nucleus
Alternating current in a circuit → radio waves of the same frequency grade 7+
Radio waves absorbed by an aerial → alternating current of the same frequency grade 7+
Ultraviolet: premature skin ageing and higher risk of skin cancer
X-rays and gamma rays: ionising; can cause mutation of genes and cancer
Radiation dose (Sv) = a measure of the risk of harm from exposure
1 Sv = 1000 mSv
How to answer each type of question
State the hazards of ultraviolet, X-rays and gamma rays
1 to 4 marks4
Ultraviolet: skin ageing prematurely and risk of skin cancer.
X-rays and gamma rays: ionising, so mutation of genes and cancer.
Use these exact effects; 'it damages you' is too vague.
Example. (a) Give two harmful effects of ultraviolet radiation on the human body. (b) Explain why X-rays can cause cancer.
Show the model answer
(a) It makes skin age prematurely (1). It increases the risk of skin cancer (1). (b) X-rays are ionising radiation (1), so they can cause mutation of genes, which can lead to cancer (1).
Convert between Sv and mSv
1 to 2 marks5
Sv to mSv: multiply by 1000.
mSv to Sv: divide by 1000.
Example. A radiographer receives a dose of 0.0035 Sv in one year. Convert this dose into millisieverts.
Show the model answer
0.0035 × 1000 (1) = 3.5 mSv (1)
Use radiation dose data to compare risks
2 to 3 marks6
Quote the numbers from the data and do the comparison (e.g. how many times bigger).
Link a bigger dose to a greater risk of harm.
If asked, weigh the benefit against the risk.
Example. A doctor can choose between two scans for a patient. A chest X-ray gives a dose of 0.02 mSv. A CT scan of the abdomen gives a dose of 8 mSv. (a) How many times greater is the dose from the CT scan? (b) Suggest why doctors only use a CT scan when it is needed.
Show the model answer
(a) 8 ÷ 0.02 = 400 times (1) (b) The CT scan gives a much bigger dose, so a greater risk of harm such as cancer (1). It should only be used when the benefit of the diagnosis outweighs this risk (1).
Explain how radio waves carry a signal (Higher tier only)
3 marks7
Transmitter: an alternating current (oscillation) produces radio waves.
State that the frequency of the waves matches the frequency of the current.
Receiver: the waves are absorbed and induce an alternating current of the same frequency.
Example. A radio transmitter sends a signal to a radio receiver. Explain how the radio waves are produced and how they produce a signal in the receiver.
Show the model answer
An alternating current (oscillation) in the transmitter's circuit produces radio waves (1) with the same frequency as the current (1). The radio waves are absorbed by the receiver's aerial and induce an alternating current with the same frequency as the radio waves (1).
Shortcuts and memory tricks
The dangerous three are at the high-frequency end: ultraviolet, X-rays, gamma rays.
Milli means a thousandth: mSv → Sv, divide by 1000; Sv → mSv, multiply by 1000.
Radio in, same frequency out: the current induced in a receiver oscillates at the frequency of the radio waves.
Where marks are lost
Describing radiation dose vaguely as 'how much radiation'. It is a measure of the risk of harm from exposure to radiation.
Confusing mSv and Sv: 5 mSv is 0.005 Sv, not 5000 Sv.
Saying gamma rays come from electrons. They come from changes in the nucleus.
Saying radio waves produce a direct current in a receiver. They induce an alternating current of the same frequency.
In data questions, writing only 'it is more dangerous' without using the numbers.
Exam technique
In data questions, quote values from the table and make a comparison, e.g. 'the CT dose is 400 times bigger'.
In risk questions, weigh up both sides: the benefit (e.g. a diagnosis) against the risk from the dose.
Name specific effects: 'skin cancer', 'mutation of genes', 'skin ageing prematurely'.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
Give one harmful effect of ultraviolet radiation on the skin.
It increases the risk of skin cancer (or causes premature ageing of the skin).
What is meant by ionising radiation?
Radiation that can knock electrons out of atoms, forming ions.
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy5 marks
Some types of electromagnetic radiation can be hazardous to human body tissue.
(a) Which two types of electromagnetic radiation are ionising? Tick (✓) two boxes.[2]
Gamma rays
Infrared
Microwaves
Visible light
X-rays
(b) Give one harmful effect of ultraviolet radiation on the skin.[1]
(c) Gamma rays are produced by changes in one part of an atom. Which part? Tick (✓) one box.[1]
The electrons
The nucleus
The outer shell
(d) Give one harmful effect of X-rays on body tissue.[1]
Show the answer and mark scheme
(a)Answer: Gamma rays; X-rays
(b)Answer: It increases the risk of skin cancer (or causes premature ageing of the skin).
makes the skin age prematurely / increases the risk of skin cancer
(c)Answer: The nucleus
(d)Answer: They can cause mutation of genes, leading to cancer.
mutation of genes / cancer
Question 2Medium8 marks
A sunbed uses lamps that emit ultraviolet radiation to tan the skin.
(a) Give two risks of using a sunbed.[2]
(b) A leaflet states that 10 minutes on a sunbed gives about the same ultraviolet dose as 1 hour in strong midday sunshine. A person uses the sunbed for 25 minutes, twice a week. Calculate the number of hours of strong midday sunshine that give the same ultraviolet dose as one week of these sunbed sessions.[2]
(c) Some sun creams absorb ultraviolet radiation. Explain how using this type of sun cream reduces the risk of harm.[2]
(d) A radiographer takes many X-ray images each day. The radiographer stands behind a lead screen when the X-ray machine is switched on. Explain why.[2]
Show the answer and mark scheme
(a)Answer: Premature ageing of the skin and an increased risk of skin cancer.
the skin ages prematurely
increased risk of skin cancer
(b)Answer: 5 hours
time on sunbed each week = 2 × 25 = 50 minutes
50 ÷ 10 × 1 = 5 (hours)
(c)Answer: The cream absorbs ultraviolet, so less reaches the skin and the dose is smaller.
less ultraviolet reaches / is absorbed by the skin (cells)
so the dose to the skin is smaller
(d)Answer: The lead absorbs X-rays; without it the radiographer's dose would build up over many images and increase the risk of cancer.
lead absorbs X-rays, so the radiographer's dose is reduced
the dose from many X-rays each day would add up, increasing the risk of gene mutation / cancer
Question 3Hard8 marks
A radio transmitter produces radio waves with a frequency of 1.2 MHz. An aerial on a radio receiver absorbs some of these radio waves. The speed of radio waves is 3.0 × 108 m/s.
(a) Describe how the radio waves are produced by the transmitter.[2]
(b) Describe the effect of the radio waves on the aerial of the receiver.[2]
(c) Calculate the period of the alternating current in the receiving aerial. Use the Physics Equations Sheet.[2]
(d) Calculate the wavelength of the radio waves.[2]
Show the answer and mark scheme
(a)Answer: An alternating current (oscillating charges) in the transmitter circuit produces radio waves of the same frequency.
oscillations (of electrons / charges) in an electrical circuit / an alternating current in the transmitting aerial
produce radio waves with the same frequency as the oscillations
(b)Answer: They induce an alternating current in the aerial with the same frequency as the waves.
the radio waves are absorbed and create / induce an alternating current in the aerial
with the same frequency as the radio waves (1.2 MHz)