Q3. A ray is incident normally on the face of an triangular prism of refracting angle of 60°. The re

Q: What is the correct answer for CUET UG Physics Q3?

The correct answer is B. If i_c is the critical angle for the prism/material, 1/μ = sin i_c. Therefore, sin i_c = 1/(√3/2) = 2/√3. This implies i_c is approximately 70.5°. However, the solution calculation gives i_c = 60° using a different interpretation (sin i_c = μ/1 for total internal reflection condition). Let's follow the solution's steps for consistency: μ = 1/sin i_c => sin i_c = 1/μ = 2/√3. For total internal refl

Q: Q3. A ray is incident normally on the face of an triangular prism of refracting angle of 60°. The refractive index of the prism is √3/2 The angle of deviation will be:

The correct answer is B. If i_c is the critical angle for the prism/material, 1/μ = sin i_c. Therefore, sin i_c = 1/(√3/2) = 2/√3. This implies i_c is approximately 70.5°. However, the solution calculation gives i_c = 60° using a different interpretation (sin i_c = μ/1 for total internal reflection condition). Let's follow the solution's steps for consistency: μ = 1/sin i_c => sin i_c = 1/μ = 2/√3. For total internal refl

Q: What are the options for this CUET UG Physics question?

A. 60° · B. 30° · C. 45° · D. 90°

Question

Q3. A ray is incident normally on the face of an triangular prism of refracting angle of 60°. The refractive index of the prism is √3/2 The angle of deviation will be:

FirstInTest · Accepted Answer

If i_c is the critical angle for the prism/material, 1/μ = sin i_c. Therefore, sin i_c = 1/(√3/2) = 2/√3. This implies i_c is approximately 70.5°. However, the solution calculation gives i_c = 60° using a different interpretation (sin i_c = μ/1 for total internal reflection condition). Let's follow the solution's steps for consistency: μ = 1/sin i_c => sin i_c = 1/μ = 2/√3. For total internal reflection, light would go from denser to rarer. If incident normally, it passes undeflected into the prism. Then it hits the second face. The angle of prism is 60°. If it's a right-angled prism, it would be 90-60-30. If the ray is normal to one face, it hits the second face at 60°. For this incidence angle, if i > i_c (for total internal reflection), it is reflected. Otherwise it refracts. i=60°. Given μ = √3/2 which is < 1. This would mean it is going from air (rarer) to denser (prism, μ>1). The question gives μ = √3/2 which is less than 1. This is physically impossible for a prism material in air. Assuming μ = 2/√3 for the prism (which is >1). Then sin i_c = 1/μ = √3/2 => i_c = 60°. A ray incident normally on the first face goes undeviated. At the second face, the angle of incidence is equal to the prism angle, 60°. Since this is the critical angle, the ray grazes the surface (emerges at 90° to normal). Thus, the angle of deviation at the second face is 90-60 = 30°. The total deviation is 30°. The solution states `sin ic = √3/2` (from μ) and `ic = 60°`. Then it says `Angle of incidence at face AC of the prism = 60°`. `Hence, refracted ray grazes the surface AC.` `Angle of emergence = 90°`. `Angle of deviation = 30°`. This implies μ = 1/(sin i_c) and sin i_c = 1. So μ=1. This is conflicting. Reinterpreting the solution to make it consistent: If the refractive index of the prism is `μ = 2/√3`. Then `sin i_c = 1/μ = √3/2`. So `i_c = 60°`. If a ray is incident normally on one face, the angle of incidence on the second face is equal to the prism angle (60°). Since this angle of incidence (60°) is equal to the critical angle (60°), the ray grazes the second surface, meaning the angle of emergence is 90°. The deviation for such a case is `δ = (i_1 - r_1) + (i_2 - r_2)`. Here `i_1 = 0, r_1 = 0`. So `δ = (i_2 - r_2)`. If `i_2 = 60°` and `r_2 = 90°` (grazing emergence), then `δ = 60° - 90° = -30°` or `30°`. So, the explanation (30°) matches option (b). The crucial assumption is μ=2/√3. The question has μ = √3/2. This is a clear typo in the question paper. I will use the solution's implied μ = 2/√3 for consistency with the provided answer and explanation.

Answer

60°

Answer

30°

Answer

45°

Answer

90°

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