The speed of light in air is 3 x 108ms-1. If the refractive index of...

JAMB 1979

The speed of light in air is 3 x 10⁸ms^-1. If the refractive index of light from air-to-water is \(\frac{4}{3}\), then which of the following is the correct value of the speed of light in water?

A. 4 x 10⁸ms^-1
B. 2.25 x 10⁸ms^-1
C. \(\frac{4}{9}\) x 10⁸ms^-1
D. 2.25 x 10²ms^-1
E. 4.33 x 10⁸ms^-1

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Correct Answer: Option B

Explanation

Air to water = \(\frac{\text{speed in air}}{\text{speed in water}}\)

\(\frac{4}{3}\) = \(\frac{3 \times 10^8}{V}\)

4V = 3(3 x 10⁸)

V = \(\frac{3(3 \times 10^8)}{4}\)

V = 2.25 x 10⁸ms^-1

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