How do waves transfer energy, and what is the electromagnetic spectrum?
Transverse and longitudinal waves, the wave equation and wave properties, the reflection of waves, the electromagnetic spectrum and its properties, and the uses and dangers of electromagnetic waves.
A focused answer to the AQA GCSE Combined Science: Trilogy Waves topic, covering transverse and longitudinal waves, the wave equation and wave properties, reflection, the electromagnetic spectrum, and the uses and dangers of electromagnetic waves.
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What this topic is asking
AQA wants you to compare transverse and longitudinal waves, use the wave equation and define wave properties, describe reflection, list the electromagnetic spectrum in order, and give the uses and dangers of electromagnetic waves.
Types of waves and the wave equation
Key wave properties: amplitude (the maximum displacement of a point from its rest position), wavelength (the distance for one complete wave, for example crest to crest), frequency (the number of waves passing a point per second, in hertz) and period (the time for one complete wave to pass, ). It is important to remember that the wave transfers energy, not matter: the particles or fields oscillate about a fixed position and do not travel with the wave.
The electromagnetic spectrum
Changes in the energy levels of electrons in atoms (and changes in the nucleus, for gamma rays) generate and absorb these waves, which is why different parts of the spectrum carry very different amounts of energy.
Uses and dangers
Uses to know, matched to the wave: radio waves for television and radio broadcasting; microwaves for satellite and mobile-phone communications and for cooking; infrared for cooking, heating, electrical heaters, infrared cameras and remote controls; visible light for seeing and for fibre-optic communication; ultraviolet for energy-efficient lamps, sun tanning and security marking; X-rays for medical imaging of bones; and gamma rays for sterilising equipment and food and for treating cancer.
The lower-frequency waves are generally safe, but the high-frequency waves carry much more energy and are ionising: ultraviolet can damage skin cells and the eyes and increase the risk of skin cancer, while X-rays and gamma rays can penetrate the body, damage cells and cause mutations or cancer. The risk depends on the dose, so radiographers limit patients' exposure and shield themselves.
Exam-style practice questions
Practice questions written in the style of AQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AQA 20193 marksA radio wave has a frequency of 200000 Hz and travels at m/s. Calculate its wavelength.Show worked answer →
A Physics Paper 2 wave-equation calculation. Method: the wave equation is , so the wavelength m. Markers award rearranging the wave equation correctly, the substitution (including handling the standard-form speed), and the answer with the unit (metres). A sense-check: radio waves have long wavelengths, so a value of around 1500 m is reasonable, whereas an answer of fractions of a metre would suggest the equation was inverted.
AQA 20214 marksThe electromagnetic spectrum is a continuous range of waves. Describe one use of microwaves and one use of infrared, and explain why ultraviolet, X-rays and gamma rays can be harmful to humans.Show worked answer →
A Physics Paper 2 question on the uses and dangers of electromagnetic waves. Reward a correct use of microwaves (satellite or mobile phone communications, or cooking food) and of infrared (cooking, heating, or remote controls and infrared cameras). For the danger: ultraviolet, X-rays and gamma rays have high frequencies and so carry a lot of energy; they are ionising, meaning they can knock electrons off atoms, which can damage cells, cause mutations and lead to cancer (ultraviolet can also damage skin and eyes). Markers credit one valid use of each named wave and the explanation that the high-frequency waves are ionising and so damage cells.
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