Question

Q. 4 If the absolute refractive index of one material is 3/4. What is the velocity the light in that material? And what will be the refractive index of another material with respect to first material when velocity of light in another material is 2.4 x 10^8 m/s ? 3 marks​

Answer 1

Answer: Speed of light in medium first is 2.5 × 10^7 m/s and refractive index of another material with respect to first material is 0.1.

Explanation:

In a medium, say medium X, absolute refractive index = nX = 3/4

Velocity of light in vacuum = c = 3 × 10^8 m/s

We know,

n-m = c/v-m

So,

v = c/n = (3 × 10^8 m/s)/(3/4)

=> vX = 2.5 × 10^7 m/s

Now, let the second medium be Y.

It is knows to us that, vY = 2.4 × 10^8 m/s

Since n21 = v1/v2,

Therefore, n-YX = vX/vY = (2.5 × 10^7)/(2.4 × 10^8) = 5/48 ≈ 0.1.

More:

• Principle of reversibility:

If it is given that the refractive index of medium 1 w.r.t. medium 2 is n. Then, refractive index of medium 2 w.r.t. medium 1 is inverse of that of medium 1 w.r.t. medium 2.

That is, n21 = 1/n12.

• Finding refractive index of medium 3 w.r.t. medium 1:

If n21, n32 is given, then:

n31 = n21 × n32

• n21 = n2/n1.