Question

The speed of light in glass is approximately ---------- that in air
100 times faster than
100 times slower than
50 per cent faster than
33 percent slower than

Answer 1

Answer on Question #46988-Physics-Optics

The speed of light in glass is approximately --- that in air

100 times faster than

100 times slower than

50 per cent faster than

33 percent slower than

Answer

The speed of light in glass is

$$v = \frac {c}{n _ {\text {g l a s s}}},$$

where $c$ is a speed of light in air, $n_{\text{glass}} = 1.5$ is the refractive index of glass.

Then

$$v = \frac {c}{1.5} = \frac {2}{3} c \approx 0.67 c \rightarrow \frac {c - v}{c} = \frac {c - 0.67 c}{c} = 0.33 = 33\%.$$

That's why the speed of light in glass is approximately 33 percent slower than that in air.

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