What's covered
Key facts
All electromagnetic waves travel at the same speed in a vacuum: 3 × 10⁸ m/s (the speed of light).
White light can be dispersed into a spectrum of colours (red, orange, yellow, green, blue, indigo, violet) by a prism because different colours (frequencies) refract by different amounts.
The amplitude of a sound wave (the size of the compression) determines its loudness — greater amplitude means a louder sound.
The amplitude is the maximum height of a wave measured from its rest (undisturbed) position.
The EM spectrum in order of increasing frequency (decreasing wavelength): radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays.
Light travels at approximately 3 × 10⁸ m/s (300,000 km/s) in a vacuum — the fastest speed possible.
An echo is the reflection of a sound wave from a surface; echoes are used in sonar to measure distances underwater.
The frequency of a wave is the number of complete waves passing a point each second.
All electromagnetic waves are transverse waves — the oscillation is perpendicular to the direction of travel; they can travel through a vacuum.
The normal is an imaginary line drawn perpendicular (at 90°) to a surface at the point where a ray hits it; angles of incidence and reflection are measured from the normal.
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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