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Discussion 1 - Refraction of light

Diagram 1




Diagram 2

Discussion

All the questions is about Snell’s Law

Remember an important point when applying the formulae

n = sin i/ sinr

sin i = the value must be taken from air even if the ray is coming it coming from a medium

sin r = value from medium

Can you tell which is the incident angle, i and the refraction angle, r when light travels from glass to air ?

refering to diagram 1

Most of us think that the a is the incident angle, i ….its not wrong to think like that but if we apply the a value as sin i then ..lets see what’s happens to the index value(n)

n=sin 30/sin 40 =0.78

its less than 1… vice versa…if I let the ray in as in diagram 2 then it will go back the same way(from air to glass with same angle) . Agree ?

so in this case…b will be the incident angle, i …so

n = sin 40/sin 30 =1.29

so which value is right ?

index value should always be more than 1 for a medium

in this case the value 1.5 is the correct one

so to avoid confusion between incident angle and refraction angle….no worries

always assume the angle in the air is the incident

from this ,

n = sin i(air)/sin r(medium) ……no matter where the ray coming from….

Answer : Question 23&24

Question 23

i. a) r = 19^◦

b) n = 1.54 …………no unit for refractive index

ii. n = 1.40

Question 24

a) c = 24.6^◦

b) n = 1/sin c = 2.4