Lesson T4.2.1

T4.2.1 Light waves and the speed of light Quiz: KS3 Physics, Unit 4

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson T4.2.1, Light waves and the speed of light: 20 multiple choice questions for the KS3 Physics (National Curriculum), Unit 4: Waves, written with Revision Ninja.

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The 20 questions

  1. What is the speed of light in a vacuum?

    • About 3 000 000 m/s, which is found by writing the speed of light with one zero too few
    • About 30 000 m/s, which is found by dropping two zeros from the correct value of the speed
    • About 300 000 000 m/s
    • About 340 m/s, which is the speed of sound in air rather than the speed of light in a vacuum

  2. Which feature of light waves differs from sound waves?

    • Light waves are slower than sound waves in air, which is why we see lightning before we hear thunder.
    • Light waves need particles to vibrate, but sound waves do not need any particles to move at all.
    • Light waves can travel through a vacuum, but sound waves cannot.
    • Light waves are longitudinal, but sound waves are transverse, which is why light travels in straight lines.

  3. Which of these is a similarity between light waves and waves in matter?

    • Both are made of solid particles that move in a circle as they carry energy through space.
    • Both always travel at the same speed in every material, whatever the material they pass through.
    • Both need a vacuum in order to travel, because the particles in matter would otherwise block them.
    • Both can be reflected and refracted.

  4. Roughly how long does sunlight take to reach the Earth?

    • About 1 second, which would be true only for a source much closer than the Sun is
    • About 8 hours, which is far too long for light moving at its very high speed through space
    • About 8 minutes 20 seconds
    • About 8 seconds, which is far too short for light to cover the distance from the Sun

  5. What is a light year?

    • The speed of light multiplied by one hour, which gives the distance light covers in a single hour.
    • The time it takes a star to shine once, which is the period of its light output over a year.
    • The distance light travels in one year, used as a unit of astronomical distance.
    • The time light takes to travel one kilometre through a vacuum of empty space between stars.

  6. Which material slows light down the most?

    • Glass, which has a higher refractive index than air
    • Empty space between stars, which is effectively a vacuum and so does not slow light at all
    • A vacuum, which is the medium in which light travels at its fastest possible speed of all
    • Air at room temperature, which slows light only slightly compared with a vacuum at all times

  7. Why does light from a distant star take many years to reach Earth?

    • The star is so far away that light takes a long time to cover the distance.
    • Light slows down in space because of the darkness, so it crawls across the empty void slowly.
    • Stars send out light only once every few years, so the light from each one arrives in a burst.
    • Light needs air in order to travel from stars, so it has to wait for air to carry it to Earth.

  8. A light wave travels 1.5 × 10¹¹ m in a vacuum. How long does it take? (Speed of light is 3 × 10⁸ m/s)

    • 500 seconds
    • 5000 seconds, which is found by dividing the distance by a speed ten times too small
    • 0.5 seconds, which is found by dividing the distance by a speed far larger than the speed of light
    • 50 seconds, which is found by dividing the distance by a speed that is too large by a factor of ten

  9. Which statement about the speed of light in air is correct?

    • It is much slower than the speed of sound in air, because air slows light much more than sound.
    • It is exactly half the speed of light in a vacuum, because the air particles halve the speed.
    • It is zero because air blocks light completely, so light cannot travel through the atmosphere.
    • It is almost the same as the speed of light in a vacuum.

  10. What type of wave is light?

    • A longitudinal pressure wave, which is carried by compressions in a medium such as air
    • A surface wave on a liquid, which is only seen as ripples on the top of a pool of water
    • A compression wave in a solid, which moves the particles of the solid back and forth in turn
    • A transverse electromagnetic wave

  11. Why can we see stars even though space is almost empty?

    • Light from stars travels through the vacuum of space to reach our eyes.
    • Stars send sound waves that our eyes can detect, which is how the stars become visible on Earth.
    • Stars make their own air, which carries their light across the empty space to our eyes.
    • Light bends around the empty space between stars, so it reaches the Earth by curving around it.

  12. Which statement about light travelling through glass is correct?

    • Light speeds up in glass and never slows down, because glass is a faster medium for light than air.
    • Light travels at the same speed in glass as in a vacuum, because glass does not affect light at all.
    • Light slows down in glass and then speeds up again on leaving it.
    • Light stops when it enters glass and restarts afterwards, which is why glass looks solid to us.

  13. Which of these is the fastest?

    • Light in glass, which is slower than light in a vacuum because the glass slows it
    • Light in a vacuum
    • Sound in air, which travels at about 340 metres per second at a normal temperature
    • Sound in water, which is faster than sound in air and in most solids that people can handle

  14. What is the best description of an electromagnetic wave?

    • A transverse wave that does not need a medium to travel.
    • A wave made of moving water particles, which carries the energy of the water across the surface.
    • A surface wave that can only move across water, which is why it is seen as ripples on a pool.
    • A longitudinal wave that needs a solid medium, because its particles have to be packed together.

  15. A light wave takes 2 seconds to travel between two points in a vacuum. What is the distance between them? (Speed of light is 3 × 10⁸ m/s)

    • 6 × 10⁸ m
    • 1.5 × 10⁹ m, which is found by dividing the speed by the time and then multiplying by ten
    • 1.5 × 10⁸ m, which is found by dividing the speed by the time instead of multiplying them
    • 6 × 10⁹ m, which is found by multiplying the speed by the time and then by a factor of ten

  16. Which of these shows light transferring energy?

    • Light passing through a clear window with no change, which shows that light is simply passing through
    • Sunlight warming a dark surface
    • A shadow that forms behind a card, which shows only that light is blocked by the card
    • A mirror that reflects light without absorbing any, which shows that light keeps its energy

  17. A student says light needs air to travel. Which observation shows that this is wrong?

    • Sunlight reaches the Earth through the vacuum of space.
    • A pool of water reflects the sky above it, because the air carries the light down to it.
    • A candle flame can be seen clearly on a windy hilltop with lots of air around it.
    • A torch beam is visible in a smoky room where the air carries the light to the viewer.

  18. Which unit is used for distances between stars?

    • Light year
    • Newton, which is the unit of force used in mechanics rather than of distance in space
    • Ampere, which is the unit of electric current in a circuit rather than of distance in space
    • Hertz, which is the unit of frequency for waves rather than of distance in space

  19. How long does light take to travel 300 000 km in a vacuum?

    • 1 minute, which uses a speed of light about sixty times smaller than the correct value
    • 0.001 seconds, which divides the distance by a speed a thousand times larger than light's
    • 1 second
    • 1 hour, which divides the distance by a speed that is far too slow for light to travel at

  20. Why does lightning appear before thunder is heard?

    • Sound travels faster than light through storm clouds, so the thunder reaches the listener first
    • Light travels much faster than sound, so it arrives first.
    • The lightning flash is delayed by the air near the ground, which slows its travel to the viewer
    • Thunder is made before the lightning flash in the storm cloud itself, so it starts earlier

All KS3 Physics quizzes