1. 11.1
Refraction of Light

2. Refraction
Refraction - the bending of light as it travels, at an angle, from a material with one refractive index to a material with a different refractive index

3. Fermat’s Principle
Fermat’s Principle – When light travels from one point to another, it follows the path that will take the least time.
1 medium = straight line More than 1 medium = bending
Example: Example:

4. Marching Band Analogy Why does light refract?
the marching band marches from an area of firm ground to mud
when one end of the band slows down, the direction of travel of the entire band changes

5. Refraction and Rays refracted ray
the ray that is bent upon entering a second medium
angle of refraction (R)
the angle between the normal and a refracted ray

6. Direction of the Refracted Ray
when a light ray travels from a medium in which its speed
is faster (air) to a medium in which its speed is slower (water) the refracted ray bends toward the normal
fast to slow – towards the normal

7. Direction of the Refracted Ray
when a light ray travels from a medium in which its speed is slower to a medium in which its speed is faster, the refracted ray bends away from the normal
slow to fast – away from the normal

8. Summary: Direction of Refraction
FAST to SLOW towards the normal Example: Air to Water
SLOW to FAST away from the normal Example: Water to Air

9. Dispersion the process of separating colours by refraction
white light (all wavelengths of visible light) refract twice:
1. when it enters the prism
2. when it leaves the prism (separates into a spectrum of colours)

10. Dispersion
each colour of light travels at a slightly different speed
only in a vacuum (space with no matter) do all colours travel at the same speed: x 108 m/s
e.g. blue light bends more than red light (blue light travels slower than red light)
Roy G. Biv

11. How much of the light refracts?
speed of light in a vacuum is
the speed of light in any other medium is less than that e.g. the speed of light in water is 2.26 x 108 m/s
3.00 x 108 m/s

12. Index of Refraction
the ratio of the speed of light in a vacuum to the speed of light in a given medium
the index of refraction is always greater than 1
as the speed of light decreases due to the medium, the index of refraction increases

13. Formula Manipulation C n V
n = C V
C = n x V
V = C n

15. Index of Refraction (n) Index of Refraction (n)
Table 11.1 Indices Pg. 454
Substance
Index of Refraction (n)
Vacuum
Gases at 0 C and kPa
Hydrogen
Oxygen
Air
Carbon dioxide
Liquids at 20 C
Water
1.333
Ethyl alcohol
1.362
Glycerol
1.470
Carbon disulfide
1.632
Substance
Index of Refraction (n)
Solids at 20 C
Quartz (fused)
1.46
Plexiglas
1.51
Glass (crown)
1.52
Sodium chloride
1.54
Glass (crystal)
Ruby
Glass (flint)
1.65
Zircon
1.92
Diamond
2.42

16. Sample Problem
Calculate the speed of light in fused quartz. The index of refraction for fused quartz is 1.46.
Equation
n = c v
n = index of refraction
c = speed of light in a vacuum
v = speed of light in a medium
Given
n = 1.46
c = 3.00 x 108 m/s
v = ?
Rearrange the equation!!!
v = c n
v = 3.00 x 108 m/s
1.46
The speed of light in fused quartz is 2.05 x 108 m/s
v = 2.05 x 108 m/s 16

17. Homework Read Section 11.1 on Pg. 449-455
Complete “Practice Problems” Pg. 455 # 1-4
Complete “Section 11.1 Review” Pg. 456 # 1-5

18. Things you need for this lesson …
Demonstration # 1:
Ray box
1 beaker + water
(Fermat’s Principle)
Demonstration # 2:
1 beaker + v. oil + water + pencil (n =C/V)
(different n’s)
Demonstration # 3:
1 beaker v. oil + 2 test tubes (same n = 1.47)