A ray of blue light passes from air into a transparent block as shown - Scottish Highers Physics - Question 13 - 2017
Question 13
A ray of blue light passes from air into a transparent block as shown.
The speed of this light in the block is
A 1.80 x 10^8 ms⁻¹
B 1.96 x 10^8 ms⁻¹
C 2.00 x 10^8 ... show full transcript
Worked Solution & Example Answer:A ray of blue light passes from air into a transparent block as shown - Scottish Highers Physics - Question 13 - 2017
Step 1
Determine the refraction angles
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Answer
Using Snell's Law:
n1imesextsin(heta1)=n2imesextsin(heta2)
where,
n1 (refractive index of air) = 1,
heta1 (angle of incidence in air) = 30°,
heta2 (angle of refraction in block) = 40°.
Plugging in the values:
1imesextsin(30°)=n2imesextsin(40°)
Solving for n2 gives us the refractive index of the block.
Step 2
Calculate the refractive index of the block
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Answer
Using the known values:
extsin(30°)=0.5,extsin(40°)≈0.6428
So,
1imes0.5=n2imes0.6428n2=0.64280.5≈0.778
Step 3
Find the speed of light in the block
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Answer
The speed of light in a medium is given by:
v=nc
where,
c (speed of light in a vacuum) = 3.00×108 ms⁻¹.
Substituting for n:
v=1.293.00×108≈2.33×108extms−1
Thus, the closest answer choice is D: 2.23×108extms−1.
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