A lightning strike gives a flash we see and a thunderclap we hear. The flash reaches us as visible light and the thunder as sound.
How are light and sound alike as waves, and how do they differ? Cover both.
Our own questions on this topic, marked straight away, so you see what to revise. Free now.
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Light is an electromagnetic wave and needs no material, so it can cross a vacuum. Sound is a mechanical wave: it moves by particles passing on vibrations, so it needs a medium and cannot cross empty space.
Light is transverse, with vibrations at right angles to the way the wave travels. Sound is longitudinal, with particles vibrating back and forth along the way the wave travels.
In air, light travels at about 3.0 × 108 m/s and sound at about 330 m/s, so light is vastly faster. Light has a much higher frequency and a much shorter wavelength than sound. Going from air into a solid, sound speeds up but light slows down.
Both kinds of wave can be reflected, refracted and diffracted, and both transfer energy without moving material along with them.
How the marks are earned
- This is level marked. For 4 to 6 marks, give accurate facts in enough detail to build a clear account. For 1 to 3 marks, give bare statements that never link up.
- Differences worth stating: light is electromagnetic and crosses a vacuum, while sound is mechanical and needs a medium; light is transverse and sound is longitudinal; light is far faster in air; light has the higher frequency and the shorter wavelength; in solids sound speeds up and light slows down.
- Similarities worth stating: both can reflect, refract and diffract, and both carry energy from place to place.
- A full account usually covers both likenesses and differences.
Why it scores
Wave type and the need for a medium are two separate differences. Each is a clear, accurate fact.
Direction of vibration is the standard way to tell the two apart, and it needs the direction named.
Quoting speeds and comparing frequency and wavelength turns a bare statement into detailed, accurate content.
Similarities are credited as well as differences. A full-mark answer has both.
Revise Wave PropertiesPick the correct relation between speed v, distance s and time t. Tick one box.
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v = s over t. Speed is distance divided by time.
How the marks are earned
- Tick the relation where speed is distance divided by time.
A lightning strike is 13 200 metres from an observer, and sound travels through air at 330 m/s. Calculate the thunder's travel time.
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Start from this equation:. speed = distance over time. Put in the values:. 330 = 13 200 over t
Rearrange to get time alone:. t = 13 200 over 330
So the time is 40 s.
How the marks are earned
- One mark: put the speed and the distance into speed = distance ÷ time.
- One mark: rearrange so time is distance divided by speed.
- One mark: the final time, 40. The unit, seconds, is not needed for the mark here, but always write it.
Why it scores
Both real values placed in the equation earn the first mark.
Time on its own on one side, with the two values on the other, earns the second mark.
The division gives the final mark. The unit is not needed for the mark here, but always write it.
Revise Sound Waves