What's covered
Key facts
Electromagnetic spectrum
All electromagnetic waves travel at the same speed in a vacuum: 3 × 10⁸ m/s (the speed of light).
Waves: transverse and longitudinal
The amplitude is the maximum height of a wave measured from its rest (undisturbed) position.
Electromagnetic spectrum
The EM spectrum in order of increasing frequency (decreasing wavelength): radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays.
Waves: transverse and longitudinal
The frequency of a wave is the number of complete waves passing a point each second.
Electromagnetic spectrum
All electromagnetic waves are transverse waves — the oscillation is perpendicular to the direction of travel; they can travel through a vacuum.
Waves: transverse and longitudinal
Frequency is measured in hertz (Hz); one hertz is one wave per second.
Electromagnetic spectrum
Gamma rays have the shortest wavelength and highest frequency; uses include killing cancer cells (radiotherapy) and sterilising medical equipment. They are highly ionising and dangerous in large doses.
Waves: transverse and longitudinal
Light (and all electromagnetic waves) are transverse waves.
Electromagnetic spectrum
Infrared radiation is emitted by warm objects; uses include thermal imaging cameras, remote controls, and toasters. Excessive exposure can cause skin burns.
Waves: transverse and longitudinal
In a longitudinal wave the oscillations are parallel to (along) the direction the wave travels, producing compressions and rarefactions.
Sample questions
A taste of the 40 questions in this topic, answers marked. Sign up to practise the full set with spaced repetition.
What do all electromagnetic waves have in common when travelling through a vacuum?
- •They all have exactly the same frequency
- •They all have exactly the same wavelength
- •They all need a solid medium to travel through
- ✓They all travel at the same speed (the speed of light)
What is the speed of light in a vacuum?
- •3,000 m/s
- •3,000,000,000 m/s
- •300,000 m/s
- ✓300,000,000 m/s
What kind of wave is sound?
- ✓Longitudinal mechanical wave
- •Standing wave only
- •Transverse electromagnetic wave
- •Transverse mechanical wave
What is a wave?
- •A liquid flowing fast
- •A solid object moving forward
- ✓Energy travelling through a medium
- •Heat radiating from the sun
Which part of the electromagnetic spectrum has the longest wavelength?
- •Gamma rays
- ✓Radio waves
- •Ultraviolet
- •X-rays
What does reflection mean for a light ray?
- •Bends when entering glass
- ✓Bounces off a surface
- •Passes through unchanged
- •Splits into many colours
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