Reflection and Refraction

Law of Reflection

• Angle of reflection = Angle of incidence

Specular vs. Diffuse Reflection

Think about bouncing a basketball on smooth surface vs. gravel road!

Refraction

http://www.upscale.utoronto.ca/PVB/Harrison/Flash/Optics/Refraction/Refraction.html

Mirage – occurs when there is a rapid shift in air density, air is hotter at surface!

Penny and Cup Activity

Index of Refraction

• Ratio of the speed of light in a vacuum to the speed of light in a particular substance

• Constant that is characteristic of a substance

Medium n = c/v

Vacuum 1.0000

Air (at STP)

1.0003

Water 1.33

Ethyl alcohol

1.36

There are no units!

Snell’s Law

• A ray bends in such a way that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant.

n1sinθ1 = n2sinθ2

Index of incident

mediumIndex of refracted

medium

refracted angleincident angle

Snell’s law examples

• 15A Q1

• 15A Question 4

• 15 131 Q1

Total Internal Reflection

• Occurs when light moves from high optically dense medium to a low optically dense medium at an angle so great there is no refracted ray

http://www.rebeccapaton.net/rainbows/tir.htm#Total%20Internal

Criteria for TIR

• High to low optically dense medium

• Angle of incidence must be greater than critical angle

Critical angle - sin θc = nr

ni

-Minimum angle of incidence for which TIR occurs

-At an instance a refracted ray moves parallel to the boundary, making θr equal to 90°