Electromagnetic spectrum
What all electromagnetic waves share, the order of the spectrum, the uses of each region and the hazards of over-exposure.
Before you begin
Radio waves, microwaves, light and X-rays are all one family of waves. This topic shows what they share, how they are arranged in order of wavelength and frequency, what each region is used for, and how over-exposure can harm the body.
Be comfortable with: frequency, wavelength and the wave equation from general wave properties.
Learning goals
- State that all electromagnetic waves are transverse
- State that all electromagnetic waves travel at the same speed in vacuum
- Order the seven electromagnetic-spectrum regions
- Relate spectrum order to wavelength and frequency
- State typical uses of radio waves
- State typical uses of microwaves
- State typical uses of infrared
- State typical uses of visible light
- State typical uses of ultraviolet
- State typical uses of X-rays
- State typical uses of gamma rays
- Describe hazardous heating effects of electromagnetic over-exposure
- Describe hazardous ionising effects on living cells and tissue
Syllabus statements covered
- state that all electromagnetic waves are transverse waves that travel with the same speed in vacuum
- describe the main regions of the electromagnetic spectrum in order of wavelength and frequency
- state examples of typical uses of the following regions of the electromagnetic spectrum: (i) radio waves (e.g. radio and television communication, astronomy and RFID tags) (ii) microwaves (e.g. mobile (cell) phones, microwave oven and satellite television) (iii) infrared (e.g. infrared remote controllers, intruder alarms and thermal imaging) (iv) visible light (e.g. photography, optical fibres in medicine and telecommunications) (v) ultraviolet (e.g. sunbeds, bank note authentication and disinfecting water) (vi) X-rays (e.g. medical radiology, security screening and industrial defect detection) (vii) gamma (γ) rays (e.g. sterilising food, detection of cancer and its treatment)
- describe how over-exposure to electromagnetic waves can have hazardous effects (e.g. heating and ionising effects of radiation) on living cells and tissue.
Lessons
Work through them in order.
Core properties & sequence
Applications & dangers
Practise and check
Recommended nextElectromagnetic spectrum topic check
Or choose
Topic reference
Quick reference
| Idea | What to remember |
|---|---|
| All electromagnetic waves | transverse; same speed in a vacuum, c = 3.0 × 10⁸ m s⁻¹ |
| Order | radio, microwaves, infrared, visible, ultraviolet, X-rays, gamma rays |
| Along the order | frequency increases, wavelength decreases |
| Wave equation | c = fλ |
| Heating hazard | microwaves and infrared: absorbed energy heats and burns tissue |
| Ionising hazard | X-rays and gamma rays: cell death, DNA damage, cancer |
| Ultraviolet hazard | sunburn, skin cancer, eye damage |
Core knowledge to remember
- All electromagnetic waves are transverse waves that travel at the same speed in a vacuum.
- In order of decreasing wavelength and increasing frequency: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays.
- Each region has typical uses: radio waves for broadcasting, microwaves for mobile phones and ovens, infrared for remote controls and thermal imaging, visible light for photography and optical fibres, ultraviolet for checking bank notes and disinfecting water, X-rays for medical images and security, and gamma rays for sterilising food and treating cancer.
- Over-exposure can harm living cells and tissue by heating or by ionisation.
Common mistakes
- Saying higher-frequency waves travel faster. All electromagnetic waves have the same speed in a vacuum.
- Mixing up the order of ultraviolet, X-rays and gamma rays.
- Giving a use without the property that makes the region suitable.
- Saying all electromagnetic waves are ionising, or that non-ionising waves are always harmless.