The Electromagnetic Spectrum (OCR GCSE Physics A (Gateway)): Flashcards
Exam code: J249
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What is an electromagnetic wave?
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Cards in this collection (48)
What is an electromagnetic wave?
An electromagnetic wave is a transverse wave that transfers energy from a source to an absorber.
True or False?
All electromagnetic waves can travel through a vacuum.
True.
All electromagnetic waves travel through a vacuum — this is why light from the Sun can reach Earth.
What is the speed of all electromagnetic waves in a vacuum?
All electromagnetic waves travel at the same speed in a vacuum: the speed of light (3 × 108 m/s).
Electromagnetic waves are all .........., they can travel through a .........., and they all travel at the .......... in a vacuum.
Electromagnetic waves are all transverse, they can travel through a vacuum, and they all travel at the same speed in a vacuum.
What is infrared radiation (energy transfer)?
Infrared radiation is emitted by all hot objects and can be absorbed by other objects, warming them up.
True or False?
Water molecules in food absorb microwave radiation, which heats the food.
True.
Water molecules absorb certain wavelengths of microwave radiation, transferring energy as heat — this is how a microwave oven works.
Why does ultraviolet radiation from the Sun benefit humans?
Ultraviolet radiation from the Sun enables humans to produce vitamin D, which is needed for healthy bones, teeth and muscles.
Complete the table showing how the Sun's EM radiation is used.
EM wave from the Sun
Effect on Earth
visible light
infrared
ultraviolet
Complete the table showing how the Sun's EM radiation is used.
EM wave from the Sun
Effect on Earth
visible light
allows living creatures to see
infrared
heats the Earth
ultraviolet
enables production of vitamin D
What is visible light?
Visible light is the range of wavelengths detectable by the human eye — it is the only part of the electromagnetic spectrum humans can see.
True or False?
Radio waves have a higher frequency than ultraviolet waves.
False.
Radio waves have a much lower frequency (and longer wavelength) than ultraviolet waves — they sit at opposite ends of the EM spectrum.
What happens to the wavelength of an EM wave as its frequency increases?
As frequency increases, wavelength decreases — the two are inversely proportional (since all EM waves travel at the same speed).
The EM spectrum in order of increasing frequency is: radio waves, microwaves, .........., visible light, ultraviolet, .......... and gamma rays.
The EM spectrum in order of increasing frequency is: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays.
What is red light (wavelength property)?
Red light has the longest wavelength in the visible spectrum and therefore the lowest frequency and energy.
Why are high-frequency EM waves more dangerous to human health than low-frequency ones?
High-frequency EM waves carry more energy and are more ionising — they can damage cells and tissues, causing mutations and cancer.
True or False?
Violet light has the shortest wavelength in the visible spectrum.
True.
Violet light has the shortest wavelength in the visible spectrum and therefore the highest frequency and energy.
Complete the table about the colours of the visible spectrum.
Colour
Wavelength (relative)
Frequency (relative)
red
violet
Complete the table about the colours of the visible spectrum.
Colour
Wavelength (relative)
Frequency (relative)
red
longest
lowest
violet
shortest
highest
What is the wave equation linking speed, frequency and wavelength?
The wave equation is v = fλ, where v is wave speed (m/s), f is frequency (Hz) and λ is wavelength (m).
State the applications of radio waves.
Radio waves are used for communication, including television broadcasts, FM radio and long-distance signal transmission.
True or False?
Microwaves are used for satellite communication and cooking food.
True.
Microwaves are used both for satellite communication (including mobile phones) and in microwave ovens to heat food.
State one use of infrared radiation in everyday life.
Infrared is used in remote controls, thermal imaging cameras and optical fibre communications to carry data.
Ultraviolet light is used in .......... lamps to detect forged banknotes. X-rays are used in .......... to see inside the body. Gamma rays are used to .......... medical equipment.
Ultraviolet light is used in fluorescent lamps to detect forged banknotes. X-rays are used in hospitals to see inside the body. Gamma rays are used to sterilise medical equipment.
True or False?
Gamma rays have no medical uses because they are too dangerous.
False.
Gamma rays are used to sterilise medical equipment and can also be used to treat cancer (radiotherapy), despite being ionising.
What is visible light used for in communication technology?
Visible light is used in optical fibres to carry data as pulses of light for high-speed internet and telephone communications.
Match each EM wave to one of its uses.
EM wave
Use
microwaves
infrared
X-rays
gamma rays
Match each EM wave to one of its uses.
EM wave
Use
microwaves
satellite communication / cooking
infrared
remote controls / thermal imaging
X-rays
medical imaging (hospitals)
gamma rays
sterilising equipment / cancer treatment
State the applications of ultraviolet (UV).
Ultraviolet light is used in fluorescent lamps, to detect forged banknotes and to sterilise water.
Define ionising radiation.
Ionising radiation is radiation with enough energy to remove electrons from atoms, forming ions — this can damage cells and DNA.
True or False?
Gamma rays are the most ionising type of electromagnetic wave.
True.
Gamma rays have the highest frequency and energy in the EM spectrum, making them the most ionising and most dangerous type.
How does ultraviolet radiation damage human skin?
Ultraviolet radiation is ionising — it can kill skin cells or cause them to mutate, leading to premature ageing and skin cancer.
Ultraviolet, .......... and gamma rays can all ionise atoms. Because of this, they can cause .......... of genes, leading to cancer.
Ultraviolet, X-rays and gamma rays can all ionise atoms. Because of this, they can cause mutation of genes, leading to cancer.
What is a radiation badge?
A radiation badge (dosimeter) is worn by workers exposed to radiation to monitor the total amount of radiation dose they receive.
Why do doctors leave the room when taking X-rays of a patient?
Doctors leave to avoid repeated exposure to X-rays — even at low doses, cumulative exposure increases the risk of cell damage and cancer.
True or False?
Microwaves are dangerous because they ionise atoms in body tissue, causing mutations.
False.
Microwaves are non-ionising and do not cause mutations. The danger from microwaves is internal heating, because they are absorbed by water molecules in the body.
What two factors affect how dangerous an EM wave is to human tissue?
The danger depends on the type of radiation (its frequency and ionising ability) and the size of the dose (the amount of exposure).
Complete the table of EM wave dangers.
EM wave
Main danger
ultraviolet
X-rays
gamma rays
microwaves
Complete the table of EM wave dangers.
EM wave
Main danger
ultraviolet
skin cancer / premature ageing / eye damage
X-rays
internal damage / gene mutation / cancer
gamma rays
cancer / cell mutation (most ionising)
microwaves
internal heating (absorbed by water)
Define ultrasound. (Higher Tier Only)
Ultrasound is sound with a frequency above 20,000 Hz (above the range of human hearing) — used for imaging hidden structures.
True or False?
Ultrasound imaging is an invasive medical procedure. (Higher Tier Only)
False.
Ultrasound is non-invasive and is believed to be harmless — it does not use ionising radiation, making it safe for imaging a foetus.
How does ultrasound detect a crack inside a metal bolt? (Higher Tier Only)
The ultrasound wave is partially reflected at the crack boundary and returns earlier than expected — the time between emission and detection reveals the crack's position.
When ultrasound reaches a boundary between two media, some waves are .......... and the rest are .......... . The .......... taken for reflections to return allows the distance to the boundary to be calculated. (Higher Tier Only)
(Higher Tier Only)
When ultrasound reaches a boundary between two media, some waves are reflected and the rest are transmitted. The time taken for reflections to return allows the distance to the boundary to be calculated.
What is an ultrasound transducer? (Higher Tier Only)
An ultrasound transducer is a device that can both emit and receive ultrasound waves — used in medical and industrial imaging.
State two medical uses of ultrasound imaging. (Higher Tier Only)
Ultrasound is used to construct images of a foetus in the womb and to generate 2D images of organs and soft tissue not surrounded by bone.
True or False?
Sound travels faster in solids than in gases. (Higher Tier Only)
True.
Sound travels fastest in solids, then liquids, then gases — the closer the particles are, the faster the sound wave travels.
Complete the table of properties that allow hidden structures to be detected using waves. (Higher Tier Only)
Property
What it means for detection
reflection
absorption
transmission
(Higher Tier Only)
Complete the table of properties that allow hidden structures to be detected using waves.
Property
What it means for detection
reflection
some of the wave bounces back at a boundary
absorption
some of the wave is taken in by the material
transmission
some of the wave passes through the material
How are radio waves produced by an alternating current? (Higher Tier Only)
Radio waves are produced when an alternating current (a.c.) of high frequency causes charge to oscillate in a transmitting antenna.
True or False?
A transmitting antenna produces radio waves by oscillating charge with a direct current (d.c.) power source. (Higher Tier Only)
False.
A transmitting antenna requires a high-frequency alternating current (a.c.) — a direct current does not oscillate and cannot produce radio waves.
What determines the frequency of the radio waves produced by a transmitting antenna? (Higher Tier Only)
The frequency of the radio waves matches the frequency of oscillation of the alternating current in the antenna — they are the same.
In a transmitting antenna, charge .......... up and down. This produces radio waves that can be absorbed by a receiving .......... some distance away. (Higher Tier Only)
In a transmitting antenna, charge oscillates up and down. This produces radio waves that can be absorbed by a receiving aerial some distance away.
What happens when a receiving aerial absorbs radio waves? (Higher Tier Only)
The radio waves induce an alternating current in the receiving aerial with the same frequency as the transmitted wave.
True or False?
The alternating current induced in a receiving aerial has the same frequency as the transmitted radio wave. (Higher Tier Only)
True.
The induced alternating current in the receiving aerial matches the frequency of the radio waves that produced it.
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