Waves, and How Light Lets Us See

Ripples on a pond, a shaking rope, a “wave” in a stadium: they all follow a pattern that moves. Let’s see what a wave carries, how to describe it, and how light lets you see the things around you.

This lesson takes about 10 minutes. You can take a break after each part.

Before you start

Waves, and How Light Lets Us See

Learning objectives

  • I can explain that a wave can make objects move, while the water or the rope stays in place.
  • I can describe a wave by its amplitude and its wavelength.
  • I can explain that we see an object when light bounces off it and enters our eyes.

What a wave carries

Waves move energy

A wave is a pattern of ups and downs that moves along. It carries energy, but the water it crosses only goes up and down.

Three pictures in a row, joined by arrows. 1: a boy drops a stone into a pond, and rings of ripples spread out toward a rubber duck. 2: the ripples reach the duck, and an arrow shows the duck going up. 3: an arrow shows the duck coming back down, in the same place on the water.
1 a stone makes ripples · 2 the duck goes up · 3 it comes back down in the same place.

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Amplitude and wavelength

Describing a wave

The high points of a wave are crests, the low points are troughs. The amplitude is how high a crest rises from the rest line. The wavelength is the distance from one crest to the next.

A blue wave line goes up and down across a dashed middle line. Number 1 marks the top of a wave, number 2 the bottom. Number 3 is an arrow from the middle line up to the top. Number 4 is an arrow from one top to the next top. Number 5 marks the dashed middle line. Number 6 is an arrow pointing to the right.
1 crest · 2 trough · 3 amplitude · 4 wavelength · 5 rest line · 6 the wave moves this way.
Four waves drawn on grids, one above the other. Waves 1, 2 and 3 have their tops the same distance apart. Wave 1 is the flattest, wave 2 the tallest, wave 3 in between. Wave 4 has its tops much closer together.
1, 2 and 3 have the same wavelength, but wave 2 has the biggest amplitude · 4 has a shorter wavelength.

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How we see things

Light into your eyes

A light source, like the Sun or a lamp, makes its own light. Most objects do not. Light from a source bounces off an object and travels into your eyes: that is how you see the object.

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Review game

Final assessment

To master the lesson, you need at least 60% correct answers.

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Summary

  • A wave is a pattern that repeats as it moves. It carries energy and can make objects move.
  • The water or the rope a wave crosses only goes up and down, in place.
  • The amplitude is the height of a crest from the rest line; the wavelength is the distance from one crest to the next.
  • A light source, like the Sun or a lamp, makes its own light.
  • We see an object when light bounces off it and enters our eyes.

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