Why colours spread out
Each colour bends by a different amount.
Red and violet
A red ray and a violet ray enter the same prism in the same direction.
What will happen to the two rays?
What this lesson covers
The idea
Different colours bend through different angles as they pass through a prism, red the least and violet the most, so each colour emerges along a different path and becomes distinct.
Red and violet
A red ray and a violet ray enter the same prism in the same direction.
What will happen to the two rays?
- They leave along different paths
- They leave along the same path
- They are both absorbed
Compare colours
Choose a colour and read the angle of deviation. The picture exaggerates the differences to make them easy to see.
Different bends
Red bends the least and violet the most, with the other colours in between. So the rays of the colours leave along different paths and become distinct. We see this band of distinct colours as the spectrum.
Different colours bend through different angles as they pass through a prism, red the least and violet the most, so each colour emerges along a different path and becomes distinct.
Notes
Different colours bend through different angles in a prism: red the least, violet the most, so each colour emerges along a different path.
Check yourself
Which colour bends the least in a prism?
Which colour bends the most in a prism?
Why does each colour become distinct in the spectrum?
- Violet. Violet bends the most.
- Red — correct. Yes!
- Yellow. Red bends the least, and violet the most.
- Red. Red bends the least.
- Blue. Violet bends the most.
- Violet — correct. Yes!
- The rays of each colour emerge along different paths — correct. Yes!
- All the colours emerge along the same path. Different colours bend through different angles, so they emerge along different paths.
- The prism adds colour to the white light. The prism does not add colour. Different colours bend through different angles and emerge along different paths.