Question

What is the velocity of light in vacuum if the velocity of light in a medium of refractive index 1.2 is \( v \, ms^{-1} \)?

• A. \( \frac{v}{1.2} \, ms^{-1} \)
• B. \( 2.4v \, ms^{-1} \)
• C. \( 1.2v \, ms^{-1} \)
• D. \( 3 \times 10^8 \, ms^{-1} \)

Hint:

Refractive index \( n = \frac{c}{v} \), so vacuum speed is always greater than medium speed.

Answer 1

The Correct Option is C

Step 1: Definition of refractive index.
\[ n = \frac{c}{v} \]

Step 2: Given refractive index.
\[ n = 1.2 \]

Step 3: Rearranging formula.
\[ c = nv \]

Step 4: Substitute values.
\[ c = 1.2 \, v \]

Step 5: Interpretation.
Speed in vacuum is greater than in medium.

Step 6: Units remain same.
Velocity remains in \( ms^{-1} \).

Step 7: Final Answer.
\[ \boxed{1.2v} \]