Light changes direction when it changes medium — Physical education, 11–13 years
Light travels at different speeds through materials such as air, water and glass. When it crosses the boundary, its direction can change, making objects under water look displaced.
Refraction bends a light path
Refraction happens when light crosses from one transparent material into another and changes speed. The change can bend its path, rather like a shopping trolley turning when one wheel reaches a rough surface first. The light has not stopped; its direction has changed at the boundary.
Why explain the bent view?
A straw in a glass can look broken, and a pool can seem shallower than it is. These observations are not tricks or errors in your eyes; light from the object has changed direction before reaching you. Refraction gives a rule for predicting the apparent position and for designing lenses.
A coin under water
Put a coin in a cup and step back until its rim hides the coin. Without moving your head, have someone pour in water. The coin becomes visible because the water bends rays from it over the rim and into your eyes. The coin stayed still; only the light path changed.
The object has not moved
It is reasonable to say that a coin under water has moved, because the image reaches your eyes from a different direction. Your brain normally assumes that light travels in straight lines, so it places the coin farther along that final direction. Refraction makes that visual estimate wrong, while the real coin remains where it was.
Lenses use refraction
Glasses, magnifying glasses, cameras and some telescopes use shaped transparent materials to refract light. Their curved surfaces bend rays so they spread out or come together in a chosen way. This can help an image form sharply on the retina, a sensor or another screen.
Keep exploring
Other languages
Loading MyLeoNes™…