Question

Light enters from air to glass having refractive index 1.2, then find the speed
light in glass. The speed of light in vacuum is 3 x 10^8 m/s.​

Answer 1

$\red{\mid{\underline{\overline{\textbf{Answer}}}\mid}}$

Speed of light in glass =

$2.5 \times {10}^{8} m/s$

$\red{\mid{\underline{\overline{\textbf{explanation}}}\mid}}$

Refractive index of a medium is the ratio of speed of light in air to speed of light in the given medium. It is defined by the expression :

$\bigstar \: \orange{\mid{\underline{\overline{\textbf{mu = vc/vm}}}\mid}}$

In this expression :

• mu = Refractive index
• Vc = Velocity of light in air
• Vm = Velocity of light in medium

There are also many ways to define Refractive index like :

mu = real depth / apparent depth

Now :-

$\blue{\mid{\underline{\overline{\textbf{Coming to question:-}}}\mid}}$

In this question we have been given the Refractive index of glass and speed of light in air, speed of light in glass is not known we have to calculate it.

Now refractive index of glass is ratio of speed of light in air to speed of light in glass.

In this question :

• Speed of light on glass = ?
• Speed of light in air = 3×10^8 m/s
• Refractive index of glass = 1.2

Now inputting the known values in expression we get :

$\mapsto \: 1.2 = \frac{3 \times {10}^{8} }{vg}$

In this expression vg is speed of light in glass.

$\mapsto \: \frac{3 \times {10}^{8} }{1.2} = \cancel \frac{3 \times {10}^{8} }{1.2}$

$\mapsto \: \cancel \frac{3000000000}{12} = 2.5 \times {10}^{8} m/s$

Therefore speed of light in glass is 2.5 × 10^8 m/s

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BY SCIVIBHANSHU

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