Grade 5 · Unit 4: The way we see things

Light changes direction

Light bends when it goes into water or glass.

The bent pencil

Put a pencil in a glass of water. It looks bent or broken at the surface! The pencil is not really bent. Light bends as it passes from water into air. This bending is called refraction.

A straw in a glass of juice also looks broken at the surface for the same reason.

Why light bends

Light travels at different speeds in air, water and glass. When it crosses from one to another at an angle, it changes direction. This makes pools and rivers look shallower than they really are.

Light slows down when it enters water or glass. Hitting the surface at an angle, one side slows first, so the light turns.

Lenses

A lens is a curved piece of glass or plastic that bends light. Magnifying glasses, spectacles, cameras and microscopes all use lenses. Your eye has a lens too.

Spectacles help people see clearly. Lenses for long sight are thicker in the middle; lenses for short sight are thinner in the middle.

Rainbows

White sunlight is a mixture of colours. A prism or raindrops bend each colour by a different amount, splitting the light into a spectrum. That is how a rainbow forms: red, orange, yellow, green, blue, indigo and violet.

You can make your own rainbow by spraying fine water drops with your back to the Sun.

What I learnt

• I know that light bends (refracts) when it passes between materials.
• I know that white light can be split into a spectrum of colours.