Physics

Speed of light in vacuum is 3 x 10⁸ m/s. Its speed in water will be :
[Given refractive index of water is 4/3]
3 x 10⁸ m/s
2.25 x 10⁸ m/s
2.5 x 10⁸ m/s
4 x 10⁸ m/s

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2.25 x 10⁸ m/s

Reason — As we know,

$μ = \dfrac{\text{Speed of light in vacuum or air (c) }}{\text {Speed of light in water (V)}} \\[0.5em]$

Given,

Refractive index of water, μ = 4/3

Speed of light in air, C = 3 × 10⁸ m / s

Substituting the values in the formula above we get,

$\dfrac{4}{3} = \dfrac{3 \times 10^8 }{V} \\[0.5em] V = \dfrac{9 \times 10^8}{4} \\[0.5em] \Rightarrow V = 2.25 \times 10^8$

Hence, Speed of light in glass = 2.25 × 10⁸ m s^-1

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