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A ray of blue light passes from air into a transparent block as shown - Scottish Highers Physics - Question 13 - 2017

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Question 13

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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)n_1 imes ext{sin}( heta_1) = n_2 imes ext{sin}( heta_2) where,

  • n1n_1 (refractive index of air) = 1,
  • heta1 heta_1 (angle of incidence in air) = 30°,
  • heta2 heta_2 (angle of refraction in block) = 40°.

Plugging in the values: 1imesextsin(30°)=n2imesextsin(40°)1 imes ext{sin}(30°) = n_2 imes ext{sin}(40°) Solving for n2n_2 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 ext{sin}(30°) = 0.5, ext{sin}(40°) \approx 0.6428

So, 1imes0.5=n2imes0.64281 imes 0.5 = n_2 imes 0.6428 n2=0.50.64280.778n_2 = \frac{0.5}{0.6428} \approx 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=cnv = \frac{c}{n} where,

  • cc (speed of light in a vacuum) = 3.00×1083.00 \times 10^8 ms⁻¹.

Substituting for nn: v=3.00×1081.292.33×108extms1v = \frac{3.00 \times 10^8}{1.29} \approx 2.33 \times 10^8 ext{ms}^{-1} Thus, the closest answer choice is D: 2.23×108extms12.23 \times 10^8 ext{ ms}^{-1}.

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