Properties of electromagnetic waves
Electromagnetic (EM) waves are produced by oscillating electric and magnetic fields. They share common properties:
- They are transverse waves.
- They can travel through a vacuum (no medium needed).
- They all travel at the same speed in a vacuum, c = 3 × 10⁸ m s⁻¹ (the speed of light).
- They transfer energy and obey v = fλ.
- They can be reflected, refracted, diffracted and show interference.
The electromagnetic spectrum
In order of increasing frequency (and decreasing wavelength):
radio waves → microwaves → infrared → visible light → ultraviolet → X-rays → gamma rays.
Higher frequency means shorter wavelength and more energy per wave.
Key formula / Key formula
For all EM waves in a vacuum: c = fλ, with c = 3 × 10⁸ m s⁻¹.
So λ = c / f and f = c / λ.
Worked example
A radio station broadcasts at a frequency of 100 MHz (1 × 10⁸ Hz). Find the wavelength of the radio wave.
λ = c / f = (3 × 10⁸) / (1 × 10⁸) = 3 m.
Uses and dangers
- Radio waves: broadcasting and communication.
- Microwaves: cooking, mobile phones, satellite links.
- Infrared: remote controls, thermal imaging, heating.
- Visible light: sight, photography, optical fibres.
- Ultraviolet: sterilising, detecting fake notes; can cause skin cancer.
- X-rays: medical imaging of bones; high doses damage cells.
- Gamma rays: killing cancer cells, sterilising equipment; very dangerous in large doses.
Remember
- All EM waves travel at c = 3 × 10⁸ m s⁻¹ in a vacuum.
- Order: radio, micro, infrared, visible, ultraviolet, X-ray, gamma.
- Higher frequency → shorter wavelength → more energy and more danger.