Refraction of light
Light changes direction when it goes into another transparent medium.
A straw in a glass of water
Light travels in straight lines in air, and in water too. But something happens at the place where air meets water.
A ray of light goes at a slant from air into water. What happens to its direction?
What this lesson covers
The idea
Light travelling obliquely from one transparent medium into another changes its direction of propagation in the second medium; this is refraction, and its extent differs for different pairs of media.
A straw in a glass of water
Light travels in straight lines in air, and in water too. But something happens at the place where air meets water.
A ray of light goes at a slant from air into water. What happens to its direction?
- It changes direction at the surface
- It carries on in exactly the same direction
- It turns back into the air
Follow the ray
Press Next step to follow a ray from air into water, and then see what a different pair of media does.
Light bends
The ray did not keep its old direction in the second medium. It bent at the surface. With glass instead of water the bend was different.
Light travelling obliquely from one transparent medium into another changes its direction in the second medium. This is refraction. The change differs for different pairs of media.
Notes
Refraction: light going obliquely into another transparent medium changes direction, by an amount that depends on the pair of media.
Check yourself
What is refraction of light?
Is the bending the same for every pair of transparent media?
Which of these is an example of refraction?
- The change in direction of light going obliquely from one transparent medium into another — correct. Yes!
- Light bouncing back from a polished surface. That is reflection. In refraction the light goes into the second medium and changes direction there.
- Light bending around a very small object. That effect is diffraction, which happens at tiny obstacles. Refraction happens when light goes into another medium.
- Yes, light bends by the same amount in water, glass and kerosene. The extent of the effect is different for different pairs of media.
- No, it is different for different pairs of media — correct. Yes!
- Yes, but only if the ray enters at a slant. The slant is needed for a change in direction, but the amount of bending still depends on the pair of media.
- A ray bouncing off a mirror back into the air. A mirror reflects light. The ray does not enter a second medium.
- A ray of sunlight moving straight through air. A ray in a single medium keeps a straight path. Refraction needs a second medium.
- A ray going from air into a glass slab at a slant and changing direction — correct. Yes!