## Friday, 5 September 2014

### REFRACTION QUESTIONS AND PROBLEMS

Refraction

Refractive index of air = 1.00, speed of light in free space = 3x108 ms-1

1. Write down Snell’s Law.

2. Define the refractive index for a transparent material.

3. Calculate the angle of refraction for the following cases:
(a) Angle of incidence 40o in air travelling into water, refractive index 1.33
(b) Angle of incidence 40o in air travelling into diamond, refractive index 2.42
(c) Angle of incidence 40o in water travelling into diamond, refractive index 2.42

4. Define the critical angle for an interface.

5. Explain what is meant by total internal reflection.

6. (a) Write down an equation that relates the critical angle to the refractive index for a material in air.
(b) How is this modified for a material in another transparent medium?

7. Calculate the critical angle for the following materials in air:
(a) Diamond       refractive index 2.42
(b) Water            refractive index 1.33
(c) Glass               refractive index 1.50

8. Calculate the critical angle for the following materials in water:
(a) Glass              refractive index 1.50
(b) Diamond      refractive index 2.42
(c) Perspex         refractive index 1.49

9. What would you expect to see if a transparent precious stone of refractive index 1.4 was immersed in a liquid of the same refractive index?

10. Draw a diagram to show the application of total internal reflection in a pair of prismatic binoculars
(b) Draw a diagram to show the application of total internal reflection in a periscope

11. (a) Why it is impossible for a ray of light to cross the corner of a 90o glass block in air? (Refractive index of glass = 1.5)
(b) Prove whether it would be possible if the block were immersed in water.

12. Explain why total internal reflection is only possible for light passing from a medium of high refractive index to one of a lower refractive index.

13. What happens to the speed of light as it passes from air into a material with a higher refractive index?

14. What happens to the wavelength of light as it passes from air into a material with a higher refractive index?

15. What happens to the frequency of light as it passes from air into a material with a higher refractive index?

16. Light travelling at 3x108 ms-1 passes into a transparent material where its speed falls to 2.2x108 ms-1.
What is the refractive index of the material?

17. A transparent material has an absolute refractive index of 1.45. What is the speed of light in the material?

18. Light travelling in the core of a glass fibre at 2x108 ms-1 meets the interface with the cladding of the fibre in which the speed of light is 2.4x108 ms-1. What is the critical angle for the core-cladding interface?