Question

If the refractive index of a prism with small prism angle is 1.6 and angle of minimum deviation is 2.4. Then prism angle of prism is ______.

• A. 4°
• B. 3°
• C. 2°
• D. 6°

Hint:

This simplified formula $(\mu - 1)A$ only works when the prism angle $A$ is small (usually less than 10°). For larger angles, you must use the full sine-based prism formula.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
For a thin prism (a prism with a very small angle $A$), the angle of minimum deviation ($\delta_m$) does not depend on the angle of incidence. It is determined solely by the refractive index ($\mu$) and the prism angle.
Step 2: Detailed Explanation:
The formula for the deviation produced by a thin prism is: $$\delta_m = (\mu - 1)A$$ Given: $\delta_m = 2.4^\circ$
$\mu = 1.6$
Substituting the values: $$2.4 = (1.6 - 1) \times A$$ $$2.4 = 0.6 \times A$$ $$A = \frac{2.4}{0.6} = 4^\circ$$
Step 3: Final Answer:
The prism angle is 4°.