Question

speed of light in glass is 2 into 10 to the power 5 kilometres per second what is the refractive index of glass​

Answer 1

given, speed of light in glass = 2*10^5 km/s = 2*10^8m/sec

we know that,

refractive index = speed in vacuum / speed in medium

n = (3*10^8) /(2*10^8)

n = (3/2)

so refractive index of glass is 3/2

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Answer 2

Given:

Speed of light = $\sf{2 \times {10}^{5} \: km/s}$

We know that:

Speed of light (in vacuum) = $\sf{3 \times {10}^{8} m/s}$

Now:

$\sf{Refractive \: index \: of \: glass:}$

$\implies$ $\sf{ \frac{Speed \: of \: light \:in \: vaccum }{Speed \: of \: light \: in \: glass}}$

$\implies$ $\sf{ \frac{3 \times {10}^{8} }{2 \times 10 ^{8} }}$

$\implies$ $\sf{ \frac{3}{2}}$

$\implies$ $\sf{1.5}$

Therefore:

Refractive index: 1.5