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Reflection and Refraction Notes

Law of Reflection

 

How large a mirror does one need to see one’s whole face? 

Microscopic

View of an

Uneven

Surface

“Diffused

Reflection” 

“o”: object 

“i”: image 

Object size, ho = Image size, hi Object distance, d o = Image distance, d i 

for a plane mirror 

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 Answer : You only need a mirror ½ the length of your face.

Law of Refraction

When light travels from one medium to another with a different refractive index, n, the light ray travels

with a different speed and so it changes direction.

A Model

   

Refractive index, n, indicates how quickly light travels in that medium…larger n = slower 

 

⏟

⏟

 

 

 

 

 

Example: Determine the angle of refraction as light travels form glass into water with an angle of 

incidence of 20.0°.

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d

() () 

()

 

()  

A similar result happens for light rays:

 Answer : The hunter should aim his spear at C, because the light reflecting off of the fish is refracted as

shown below. Our eyes perceive light as travelling in straight lines, so the fish appears to be at B even

though it is really at C.

Where does the hunter 

aim his spear if the fishappears as it is shown?

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Questions on Refraction

Light is incident on a glass prism (n = 1.50) and the incident angle, θ i is 35°. Determine

a)  the angle of refraction, θ r at A.

 b)  the angle of incidence, θ i at B.

c)  the angle of refraction, θ r at B.

(nair = 1.0003)

a)  At A:  

 

 

 b)  At B: ( )  

c) 

at B:  

 

Critical Angle and Total Internal Reflection

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Question: Determine the critical angle for water (nwater = 1.33, nair = 1.00).

 

 

Glass or Diamond?

nair = 1.00

nglass = 1.50

ndiamond = 2.42

A diamond sparkles more as the light

reflects internally more than glass

does. Different colours have slightly

different refractive indices and thus, a

spectrum of colour is often refracted

out of the diamond - dispersion.

What is a mirage?

( ) 

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Since we always see light rays travelling in straight lines…The sun and clouds appear as a reflection as

though there is some water on the ground. This illusion is called a MIRAGE.

How is a rainbow formed? Read up about it.