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Light and sound carry energy

Energy and power · level 2, lesson 6 of 6

A question to start

Sunshine through a magnifying glass can make a spot hot enough to burn paper. A loud bang can rattle a window. How can light and sound do things, when you cannot hold them?

The idea

Light and sound are ways of carrying energy from one place to another.

  • Light carries energy from the Sun, a fire or a lamp, through the air and even through empty space. When it lands on something, some of its energy turns into heat, or into electricity in a solar panel, or into food in a leaf.
  • Sound carries energy as tiny shakes, called vibrations, passing through the air (or water, or a wall). Your ears catch a little of that energy and turn it into what you hear.
light crosses empty spacesound needs air orsomething to travel in

There is one big difference. Light can travel through empty space; that is how sunlight gets to us. Sound cannot: it needs something to travel through. In space, there is no sound at all.

On Mars, sunlight reaches the ground, weaker than on Earth. Sound travels too, but the air is so thin that it carries much less energy. Voices and noises on Mars are much quieter than on Earth, and fade quickly with distance. The rover Perseverance has microphones, and has recorded the wind, its own wheels, and the hum of the helicopter Ingenuity.

Worked examples

1. Solar panels. They catch light energy and turn it into electrical energy.

2. A loudspeaker. It turns electrical energy into sound energy by making the air vibrate.

3. Thunder and lightning. A lightning flash gives out light, heat and sound. You see the flash first, because light travels much faster than sound.

Try it

  1. Name two things that light energy can turn into when it lands on something.
  2. What does sound need to travel through?
  3. Could you hear an explosion in empty space?
  4. Why are sounds on Mars quieter than on Earth?
Answers
  1. For example: heat, electricity (in a solar panel), food (in a leaf).
  2. A material: air, water or a solid.
  3. No: there is nothing for the sound to travel through.
  4. The air there is very thin, so it carries much less sound energy.

Common mistake

"Space is full of noise, like in films." Space is silent: with nothing to carry vibrations, sound cannot travel there. The rumbles of spaceships in films are added for effect.

Where it leads