Hi Farhaini,
SPM Physics Light & Optics
- Figure 10 shows a ray is refracted through a prism.
Determine the refractive index of prism that is shown in below.
A 0.68
B 0.82
C 1.23
D 1.46
SPM Physics Light & Optics Solution
This question is related to Snell’s Law:
Img source: Wikipedia Oleg Alexandrov
Formula
From figure above, we can find the incident angle by recognising the “c” pattern of 2 parallel lines. The x + y inside “c” must be equal to 180 degree.
Applying the formula,
Refractive index = sin\theta_1 / sin\theta_2
where \theta_1 is angle from less dense medium (air), \theta_2 is angle from denser medium glass prism.
Refractive index of prism = sin(70) / sin(40) = 1.46
Answer: D
Thank you very much!
Is it wrong if I use this formula?
n = sin r
--------
sin I
n= sin 70
-----------
sin 40
n=1.46
You are correct, I made a mistake, sorry
Since we are finding refractive index of prism, the angle on top of fraction should be angle from the less dense medium, which is air, so should be sin(70) / sin(40).
Refractive index of glass prism normally should be greater than 1, because it is denser than air.
I have edited my solution to reflect this changes
It’s okay. Thank you so much. 