13.2 Refraction  (Page 3/3)

Both these situations can be seen in [link] .

What happens to a ray that lies along the normal line? In this case, the angle of incidence is $0^{\circ }$ and

This shows that if the light ray is incident at $0^{\circ }$ , then the angle of refraction is also $0^{\circ }$ . The ray passes through the surface unchanged, i.e. no refraction occurs.

Investigation : snell's law 1

The angles of incidence and refraction were measured in five unknown media and recorded in the table below. Use your knowledge about Snell's Law to identify each of the unknown media A - E. Use [link] to help you.

Investigation : snell's law 2

Zingi and Tumi performed an investigation to identify an unknown liquid. They shone a beam of light into the unknown liquid, varying the angle of incidence and recording the angle of refraction. Their results are recorded in the following table:

1. Write down an aim for the investigation.
2. Make a list of all the apparatus they used.
3. Identify the unknown liquid.
4. Predict what the angle of refraction will be for 70 ${}^{\circ }$ , 75 ${}^{\circ }$ , 80 ${}^{\circ }$ and 85 ${}^{\circ }$ .

Apparent depth

Imagine a coin on the bottom of a shallow pool of water. If you reach for the coin, you will miss it because the light rays from the coin are refracted at the water's surface.

Consider a light ray that travels from an underwater object to your eye. The ray is refracted at the water surface and then reaches your eye. Your eye does not know Snell's Law; it assumes light rays travel in straight lines. Your eye therefore sees the image of the at coin shallower location. This shallower location is known as the apparent depth .

The refractive index of a medium can also be expressed as

Refraction

1. Explain refraction in terms of a change of wave speed in different media.
   
2. In the diagram, label the following:
   1. angle of incidence
   2. angle of refraction
   3. incident ray
   4. refracted ray
   5. normal

   

3. What is refraction?
   
4. Describe what is meant by the refractive index of a medium .
   
5. State Snell's Law.
   
6. In the diagram, a ray of light strikes the interface between two media.

   

   Draw what the refracted ray would look like if:
   1. medium 1 had a higher refractive index than medium 2.
   2. medium 1 had a lower refractive index than medium 2.
7. Light travels from a region of glass into a region of glycerine, making an angle of incidence of 40 ${}^{\circ }$ .
   1. Describe the path of the light as it moves into the glycerine.
   2. Calculate the angle of refraction.
8. A ray of light travels from silicon to water. If the ray of light in the water makes an angle of 69 ${}^{\circ }$ to the surface normal, what is the angle of incidence in the silicon?
   
9. Light travels from a medium with $n=1,25$ into a medium of $n=1,34$ , at an angle of 27 ${}^{\circ }$ from the interface normal.
   1. What happens to the speed of the light? Does it increase, decrease, or remain the same?
   2. What happens to the wavelength of the light? Does it increase, decrease, or remain the same?
   3. Does the light bend towards the normal, away from the normal, or not at all?
10. Light travels from a medium with $n=1,63$ into a medium of $n=1,42$ .
    1. What happens to the speed of the light? Does it increase, decrease, or remain the same?
    2. What happens to the wavelength of the light? Does it increase, decrease, or remain the same?
    3. Does the light bend towards the normal, away from the normal, or not at all?
11. Light is incident on a glass prism. The prism is surrounded by air. The angle of incidence is 23 ${}^{\circ }$ . Calculate the angle of reflection and the angle of refraction.
    
12. Light is refracted at the interface between air and an unknown medium. If the angle of incidence is 53 ${}^{\circ }$ and the angle of refraction is 37 ${}^{\circ }$ , calculate the refractive index of the unknown, second medium.
    
13. A coin is placed in a bowl of acetone ( $n$ = 1,36). The coin appears to be 10 cm deep. What is the depth of the acetone?
    
14. A dot is drawn on a piece of paper and a glass prism placed on the dot according to the diagram.

    

    Use the information supplied to determine the refractive index of glass.
    
15. Light is refracted at the interface between a medium of refractive index 1,5 and a second medium of refractive index 2,1. If the angle of incidence is 45 ${}^{\circ }$ , calculate the angle of refraction.
    
16. A ray of light strikes the interface between air and diamond. If the incident ray makes an angle of 30 ${}^{\circ }$ with the interface, calculate the angle made by the refracted ray with the interface.
    
17. Challenge Question : What values of $n$ are physically impossible to achieve? Explain your answer. The values provide the limits of possible refractive indices.
    
18. Challenge Question : You have been given a glass beaker full of an unknown liquid. How would you identify what the liquid is? You have the following pieces of equipment available for the experiment: a laser, a protractor, a ruler, a pencil, and a reference guide containing optical properties of various liquids.