Physics Q41 – JEE-MAIN 2025

Consider following statements for refraction of light through prism, when angle of deviation is minimum. A. The refracted ray inside prism becomes parallel to the base. B. Larger angle prisms provide smaller angle of minimum deviation. C. Angle of incidence and angle of emergence becomes equal. D. There are always two sets of angle of incidence for which deviation will be same except at minimum deviation setting. E. Angle of refraction becomes double of prism angle. Choose the correct answer from the options given below:

Clue 1 of 3: Conditions for Minimum Deviation

Recall the specific conditions that apply to the path of light and angles when a prism is at minimum deviation.

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Ninja Strategy•Recall Key Conditions

Recalling the fundamental conditions for minimum deviation (ray parallel to base, $i = e$ , $r = A / 2$ ) quickly identifies correct statements A, C, and the incorrect statement E, allowing for rapid elimination.

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Step 1: Analyze conditions for minimum deviation✦ Active

At minimum deviation ( $δ_{m}$ ) for a prism, the following conditions hold:

1. The angle of incidence ( $i_{1}$ ) is equal to the angle of emergence ( $i_{2}$ ). So, $i_{1} = i_{2} = i$ .

2. The angles of refraction at both surfaces are equal. So, $r_{1} = r_{2} = r$ .

3. The refracted ray inside the prism is parallel to the base of the prism.

4. From the prism formula $A = r_{1} + r_{2}$ , it follows that $A = 2 r$ , so $r = A / 2$ .

Step 2: Evaluate each statement○ Expand

A. The refracted ray inside prism becomes parallel to the base. This is TRUE, as per the conditions for minimum deviation.

B. Larger angle prisms provide smaller angle of minimum deviation. This is FALSE. For a given material, generally, a larger prism angle ( $A$ ) leads to a larger angle of minimum deviation ( $δ_{m}$ ). For small angles, $δ_{m} = (n - 1) A$ where $n$ is the refractive index.

C. Angle of incidence and angle of emergence becomes equal. This is TRUE, as per the conditions for minimum deviation ( $i_{1} = i_{2}$ ).

D. There are always two sets of angle of incidence for which deviation will be same except at minimum deviation setting. This is TRUE. The graph of deviation versus angle of incidence is symmetric around the minimum deviation point. For any deviation greater than the minimum, there are two distinct angles of incidence that produce that same deviation.

E. Angle of refraction becomes double of prism angle. This is FALSE. At minimum deviation, the angle of refraction ( $r$ ) is half of the prism angle ( $A$ ), i.e., $r = A / 2$ .

Step 3: Identify correct statements and choose the option○ Expand

Based on the evaluation, statements A, C, and D are correct. Therefore, the option that includes A, C, and D only is the correct answer.

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Physics Question 41 – JEE-MAIN 2025

Clue 1 of 3: Conditions for Minimum Deviation

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