Refraction of Light
Simple Explanation
Refraction is the bending of light as it passes from one medium into another (e.g. air into glass), caused by light changing speed at the boundary. Light bends toward the normal when slowing down (entering a denser medium) and away from the normal when speeding up (entering a less dense medium).
Why Do We Need It?
Refraction is the basic phenomenon underlying lenses, prisms, and countless optical instruments — understanding why and how light bends is essential before quantifying it with laws and formulas.
Why Does This Work?
When light enters a new medium at an angle, one 'edge' of the light wavefront reaches the new, slower (or faster) medium before the rest — this causes the wavefront to pivot, changing the direction of travel, similar to how a car's wheels turn if one side rolls onto a rougher (slower) surface before the other.
Real-Life Example
A straw appearing bent in a glass of water
A straw placed in a glass of water appears to bend sharply at the water's surface.
Light from the submerged part of the straw refracts (bends) as it exits the water and enters the air, changing direction at the surface — this bending distorts the apparent position of the submerged part, making the straw look bent, even though it is perfectly straight.
Practice
What causes light to bend when it enters a new medium at an angle?
MediumCommon mistake
Assuming light always bends toward the normal — it only bends toward the normal when entering a DENSER (slower) medium; it bends AWAY from the normal when entering a LESS DENSE (faster) medium.
Quick Review
- Refraction: bending of light at a boundary between media, due to a change in speed.
- Denser medium (slower light) → bends toward the normal.
- Less dense medium (faster light) → bends away from the normal.