The Electromagnetic Spectrum
The electromagnetic (EM) spectrum is a continuous family of transverse waves that all travel at the same speed through a vacuum, 3 x 10^8 m/s, but have a huge range of wavelengths and frequencies. In order of increasing frequency, the seven regions are radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays, with the highest-frequency waves, ultraviolet, X-rays and gamma rays, being ionising and able to damage cells and DNA.
Method
- Memorise the order of the seven regions from longest wavelength to shortest: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays.
- Remember that all EM waves are transverse and all travel at the same speed in a vacuum (and approximately the same speed in air), 3 x 10^8 m/s, so use v = f x wavelength with this fixed speed to convert between frequency and wavelength for any region.
- Learn one everyday or technological use for each region: radio waves for broadcasting and communication; microwaves for satellite communication and cooking food; infrared for cooking, thermal imaging cameras and short-range communication such as remote controls; visible light for vision and fibre optic communication; ultraviolet in energy-efficient lamps and for producing vitamin D in skin; X-rays for imaging bones and airport security scanners; gamma rays for sterilising medical equipment and treating cancer.
- Learn the matching risk for each higher-energy region: ultraviolet exposure can cause skin to age prematurely and increases the risk of skin cancer; X-rays and gamma rays are ionising radiation, meaning they can damage or mutate DNA inside cells, which can lead to cancer, so exposure is minimised, for example using lead aprons and shielding in hospitals.
- For questions on how EM waves are produced or absorbed, connect each region to a mechanism: changes in the nucleus of an atom emit gamma rays; changes in the electron energy levels of an atom can emit or absorb ultraviolet, visible and infrared radiation.
- In calculation questions, check which quantity you are given and which you need, then rearrange v = f x wavelength (using the triangle: cover the one you want to find), and convert wavelengths given in nm, um or mm into metres before substituting.
- For 'explain the risk' style questions, name the specific type of wave, name the specific type of biological damage (cell/DNA damage, mutation, cancer, skin damage) and link the size of the risk to the size of the dose (how long or how much exposure).
Worked example
A radio station broadcasts at a frequency of 100 000 000 Hz (100 MHz). Electromagnetic waves travel at 3 x 10^8 m/s. Calculate the wavelength of the radio waves.
- Write the wave equation: wave speed = frequency x wavelength (v = f x wavelength).
- Rearrange to find wavelength: wavelength = v / f.
- Substitute the values: wavelength = (3 x 10^8) / (100 000 000).
- Since 100 000 000 = 1 x 10^8, calculate: wavelength = (3 x 10^8) / (1 x 10^8) = 3.
- Final answer: the wavelength is 3 m, a realistic wavelength for FM radio waves.
Practice questions
Type your answer and press Check to be marked straight away, or reveal the answer and mark yourself.
Q1State the seven regions of the electromagnetic spectrum in order of increasing frequency.Show answer
Answer: Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays.
Q2State the speed of all electromagnetic waves travelling through a vacuum.Show answer
Answer: 3 x 10^8 m/s
Q3Name the type of electromagnetic wave used by a television remote control.Show answer
Answer: Infrared.
Q4Explain why ultraviolet, X-rays and gamma rays can be hazardous to human health, but radio waves are not.Show answer
Answer: Ultraviolet, X-rays and gamma rays carry enough energy to be ionising, meaning they can remove electrons from atoms and damage or mutate DNA in cells, which can lead to skin damage or cancer; radio waves have much lower frequency and energy and do not ionise atoms.
Q5A microwave oven uses electromagnetic waves with a wavelength of 0.12 m. Calculate the frequency of these waves (speed of light = 3 x 10^8 m/s).Show answer
Answer: 2.5 x 10^9 Hz (f = v/wavelength = 3x10^8 / 0.12 = 2.5x10^9 Hz)
Q6Name the type of electromagnetic wave used to treat cancer by killing cells in a tumour, and state which part of the atom emits it.Show answer
Answer: Gamma rays; they are emitted from changes inside the nucleus of an unstable (radioactive) atom.
Q7State one medical use of X-rays and one safety precaution taken when X-rays are used in a hospital.Show answer
Answer: Medical use: imaging broken bones (or other dense objects inside the body). Safety precaution: staff stand behind a lead or lead-lined screen, or wear a lead apron, to reduce their exposure.
Q8An X-ray has a wavelength of 1 x 10^-10 m. Calculate its frequency (speed of light = 3 x 10^8 m/s).Show answer
Answer: 3 x 10^18 Hz (f = v/wavelength = 3x10^8 / 1x10^-10 = 3x10^18 Hz)
Exam-style questions
Written in the style of a GCSE Science exam paper, with a full mark scheme.
A Wi-Fi router transmits microwaves with a frequency of 2.4 x 10^9 Hz. Calculate the wavelength of these microwaves (speed of electromagnetic waves = 3 x 10^8 m/s). Give your answer to 2 significant figures.
Show mark scheme
Tick each line you got. Your score builds from the marks on the scheme.
Nothing ticked yet - 3 available
State two differences between infrared radiation and ultraviolet radiation.
Show mark scheme
Tick each line you got. Your score builds from the marks on the scheme.
Nothing ticked yet - 2 available
A hospital uses X-rays to image a patient's broken arm, and uses gamma rays to treat a different patient's cancer. Explain, in terms of energy and ionisation, why both of these waves are useful in medicine despite being hazardous, and describe one precaution used to protect staff or patients from unwanted exposure.
Show mark scheme
Tick each line you got. Your score builds from the marks on the scheme.
Nothing ticked yet - 6 available
See real GCSE Science past-paper questions, with official mark schemes →
Free printable worksheet
Want more practice on paper? Download the the electromagnetic spectrum worksheet pack - 12 pages of exam-style questions with a full mark scheme. One email opens every download in this browser for 14 days - no account, no card. Print it for personal and classroom use.
This topic is chapter 19 of GCSE Physics Workbook, the whole course as one free printable PDF.
Next topics
Not quite what you needed?
Tell us what is missing on the electromagnetic spectrum, or which topic to write up next. Every request is read, and we reply to every one.
Build a full practice pack.
This topic is one of hundreds in the library - pick the ones a student needs and generate a printable PDF in minutes.