1. Look at your work from last lesson…
Learning Objectives
By the end of this lesson you should be able to…
Define the refractive index in terms of;
n = 1 / critical angle
n = c / v
n = sin i / sin r
Explain how dispersion is a result of different refractive indices in white light.
Practice using equations for refraction and drawing ray diagrams.
Look at your work from last lesson…
What do you notice about the value you get if you find / sine of critical angle for Perspex.
Why is this number familiar?

2. Learning Objectives
By the end of this lesson you should be able to…
Define the refractive index in terms of;
n = 1 / critical angle
n = c / v
n = sin i / sin r
Explain how dispersion is a result of different refractive indices in white light.
Practice using equations for refraction and drawing ray diagrams.
Refractive Index
The refractive index of a medium can be found by dividing the sine of the critical angle by 1. This makes sense since the amount of refraction seen is a result of the refractive index.

3. Refractive Index Learning Objectives
By the end of this lesson you should be able to…
Define the refractive index in terms of;
n = 1 / critical angle
n = c / v
n = sin i / sin r
Explain how dispersion is a result of different refractive indices in white light.
Practice using equations for refraction and drawing ray diagrams.
Refractive Index
Material
Refractive Index (n)
Working
Critical angle (c)
Glass
1.5
Water
1.33
Diamond
2.42

4. Define the refractive index in terms of;
Learning Objectives
By the end of this lesson you should be able to…
Define the refractive index in terms of;
n = c sin i
sin c v sin r
Explain how dispersion is a result of different refractive indices in white light.
Practice using equations for refraction and drawing ray diagrams.

5. Calculating Refractive Index
Learning Objectives
By the end of this lesson you should be able to…
Define the refractive index in terms of;
n = 1 / critical angle
n = c / v
n = sin i / sin r
Explain how dispersion is a result of different refractive indices in white light.
Practice using equations for refraction and drawing ray diagrams.
Calculating Refractive Index
The refractive index, n, tells you the extent to which the medium will refract light – it is a function of the way light interacts with the medium.
n = 1 c sin i sin c v sin r
Where:
i = the angle of incidence
r = angle of refraction
c = speed of light in vacuum
v = speed of light in medium
Sin c = critical angle

6. Learning Objectives
By the end of this lesson you should be able to…
Define the refractive index in terms of;
n = 1 / critical angle
n = c / v
n = sin i / sin r
Explain how dispersion is a result of different refractive indices in white light.
Practice using equations for refraction and drawing ray diagrams.
Example The Refractive index of glass is 1.5. If the angle of incidence of a light ray is 35o, calculate the angle of refraction.

7. Learning Objectives
By the end of this lesson you should be able to…
Define the refractive index in terms of;
n = 1 / critical angle
n = c / v
n = sin i / sin r
Explain how dispersion is a result of different refractive indices in white light.
Practice using equations for refraction and drawing ray diagrams.
Example Light travels through stained glass at 1.8 x 108 m/s. What is the refractive index of stained glass?

8. Now try the sheet! Learning Objectives
By the end of this lesson you should be able to…
Define the refractive index in terms of;
n = 1 / critical angle
n = c / v
n = sin i / sin r
Explain how dispersion is a result of different refractive indices in white light.
Practice using equations for refraction and drawing ray diagrams.
Now try the sheet!

9. Dispersion Learning Objectives
By the end of this lesson you should be able to…
Define the refractive index in terms of;
n = 1 / critical angle
n = c / v
n = sin i / sin r
Explain how dispersion is a result of different refractive indices in white light.
Practice using equations for refraction and drawing ray diagrams.
Dispersion

10. Dispersion In a vacuum all electromagnetic waves travel at
Learning Objectives
By the end of this lesson you should be able to…
Define the refractive index in terms of;
n = 1 / critical angle
n = c / v
n = sin i / sin r
Explain how dispersion is a result of different refractive indices in white light.
Practice using equations for refraction and drawing ray diagrams.
Dispersion
In a vacuum all electromagnetic waves travel at
the same speed, but when they travel into a
denser medium they slow down.

11. Learning Objectives
By the end of this lesson you should be able to…
Define the refractive index in terms of;
n = 1 / critical angle
n = c / v
n = sin i / sin r
Explain how dispersion is a result of different refractive indices in white light.
Practice using equations for refraction and drawing ray diagrams.
Dispersion
The speed an electromagnetic wave travels at through a material varies slightly with the frequency (colour) of the light. Therefore, within a material, different colours of light travel at different speeds.

12. Learning Objectives
By the end of this lesson you should be able to…
Define the refractive index in terms of;
n = 1 / critical angle
n = c / v
n = sin i / sin r
Explain how dispersion is a result of different refractive indices in white light.
Practice using equations for refraction and drawing ray diagrams.
Dispersion
The higher the frequency of the light the more it will slow down when it travels through a material therefore...
Red, lower frequency, will be slowed the least,
Violet , highest frequency, slowed the most.
n = 1.48
n = 1.51

13. n = 1.48 n = 1.51 Learning Objectives
By the end of this lesson you should be able to…
Define the refractive index in terms of;
n = 1 / critical angle
n = c / v
n = sin i / sin r
Explain how dispersion is a result of different refractive indices in white light.
Practice using equations for refraction and drawing ray diagrams.
Using the refractive indices of the different wavelengths of light below calculate the angle of refraction if white light is incident on a glass prism at 43°
If the wavelength of red light is X and the wavelength of violet is X. Green light has a wavelength of X; predict a refractive index for green light and calculate its angle of incidence.
Todays Noodle Tickler: Based on the value from No. 1 how wide would the rainbow colour beam be 1m after the prism?
n = 1.48
n = 1.51