What is the electromagnetic spectrum, and what are the uses and hazards of each type of wave?
The electromagnetic spectrum from radio to gamma, its order by wavelength, frequency and energy, the common properties of all electromagnetic waves, and the uses and hazards of each part.
A focused answer to OCR Gateway GCSE Physics A topic P5 on the electromagnetic spectrum, covering the order from radio to gamma by wavelength, frequency and energy, the common properties of all electromagnetic waves, and the uses and hazards of each part.
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What this topic is asking
OCR wants you to put the electromagnetic spectrum in order, state the common properties of all electromagnetic waves, and give the uses and hazards of each part. This is topic P5.2 of the OCR Gateway Physics A (J249) specification.
The order of the spectrum
A common way to remember the order is a mnemonic for Radio, Microwave, Infrared, Visible, Ultraviolet, X-rays, Gamma. Visible light is only a tiny part of the whole spectrum, ranging from red (longest wavelength) to violet (shortest).
Common properties of all electromagnetic waves
Because they all travel at the same speed in a vacuum, shows that a higher frequency must mean a shorter wavelength across the spectrum.
Uses of each part
- Radio waves: television and radio broadcasting, and long-distance communication.
- Microwaves: cooking food (water absorbs them and heats up) and satellite and mobile-phone communications.
- Infrared: heating, cooking (grills, toasters), thermal imaging cameras, and remote controls and short-range optical-fibre links.
- Visible light: seeing, photography, and communication along optical fibres.
- Ultraviolet: security marking (invisible ink that glows), detecting forged banknotes, sun tanning, and sterilising water.
- X-rays: medical images of bones, checking welds and airport security scans.
- Gamma rays: sterilising medical equipment and food, detecting and treating cancer (radiotherapy), and use as medical tracers.
Hazards of the high-energy waves
This is why radiographers stand behind shielding when taking X-rays, why sunscreen blocks ultraviolet, and why exposure to ionising radiation is kept as low as reasonably possible.
Try this
Q1. State which part of the electromagnetic spectrum has the highest frequency. [1 mark]
- Cue. Gamma rays.
Q2. State one use of infrared radiation. [1 mark]
- Cue. Heating, thermal imaging, or remote controls (any one).
Exam-style practice questions
Practice questions written in the style of OCR exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
OCR 20194 marksList the seven groups of the electromagnetic spectrum in order from the longest wavelength to the shortest, and state one use of microwaves and one use of X-rays.Show worked answer →
A P5 question worth four marks. In order from longest wavelength (lowest frequency) to shortest wavelength (highest frequency): radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays (2 marks for the full correct order). A use of microwaves: cooking food or satellite and mobile-phone communications (1 mark). A use of X-rays: producing images of bones in medicine or checking welds and luggage (1 mark). Markers reward the correct order across all seven groups and a valid use of each named type. A common error is to reverse the order or to swap infrared and ultraviolet.
OCR 20213 marksUltraviolet, X-rays and gamma rays can be hazardous to the human body. Explain why these waves are more dangerous than radio waves and visible light.Show worked answer →
A P5 Explain question worth three marks. Ultraviolet, X-rays and gamma rays are at the high-frequency, short-wavelength end of the spectrum, so they carry much more energy per wave (1 mark). This high energy means they are ionising: they can knock electrons off atoms, damaging cells and DNA, which can cause mutations and cancer (1 mark). Radio waves and visible light have much lower energy and are not ionising, so they do not damage cells in this way (1 mark). Markers reward the link from high frequency to high energy, the ionising damage to cells and DNA, and the contrast with the low-energy, non-ionising waves. A common error is to say all electromagnetic waves are equally dangerous.
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