Light refracts when passing from one medium to another with a different density. When light travels from a less dense to a more dense medium, it bends toward the normal, and when traveling from more dense to less dense, it bends away from the normal. The refractive index is a ratio of the speed of light in a vacuum to the speed in a particular medium, and is represented by the Greek letter μ. Snell's law describes the relationship between the angles of incidence and refraction.

2. Examples from daily life

5. Points to remember
 When a ray light passes from air to water its speed changes. Due to this
there is a change in direction of the ray
 The change in direction suffered by a ray of light as passes obliquely from
one optical medium to another with different optical densities is known as
refraction
 When a ray of light is incident on a surface separating two media a small
fraction of light always get reflected.
 Refraction can make an object appear to be on a different position

6. Why does light refract?
Why does light refract?

7. when a ray of light goes from an optically rarer medium to an optically
denser medium, the speed of light decreases and the light ray bends towards
the normal.

9. When a ray of light travels from a denser medium to a rarer medium, the ray
of light bends away from the normal.

10. Refraction through a glass slab

11. Effects of refraction

14. Twinkling of stars

15. Variation in the size of sun at dusk,
dawn and at noon.

16. Refractive index
• The ability to refract light is called refractive index.
• Refractive index of a medium is equal to the ratio of speed of light in
vacuum to the speed of light in that particular medium
• This ratio is a constant for a given pair of media.
• It is represented by a greek letter ‘μ’

17. Snell’s law of refraction

18. Thank you