Question

For the same angle of incidence, the angles of refraction in media A, B, C and D are \(50^{\circ }\), \(40^{\circ }\), \(30^{\circ }\) and \(20^{\circ }\) respectively. The speed of light is minimum in medium

• A. A
• B. B
• C. C
• D. D

Hint:

Use Snell's law: for the same angle of incidence, a smaller angle of refraction means a larger refractive index and a lower speed.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept
By Snell's law \(\mu=\frac{\sin i}{\sin r}\), and the speed of light in a medium is \(v=\frac{c}{\mu}\).

Step 2: Compare the media
The angle of incidence is the same for all four media, so \(\mu\propto\frac{1}{\sin r}\).
The smallest angle of refraction gives the largest refractive index.

Step 3: Find the minimum speed
The angles are \(50^{\circ}, 40^{\circ}, 30^{\circ}, 20^{\circ}\), so medium D (\(20^{\circ}\)) has the largest \(\mu\).
Since \(v=\frac{c}{\mu}\), the speed is least in D.

Final Answer:
The speed of light is minimum in medium D. \[ \boxed{\text{(D) }D} \]