Question

Time taken by a ray of light to travel through a glass slab of thickness 10 cm and refractive index 1.5 will be (Take c = 3 × 10 8 m/s)
(A) 4.5 × 10 -10 s
(B) 10 -7 s
(C) 5 × 10 -8 s
(D) 5 × 10 -10 s

Answer 1

Explanation:

n=c/v

1.5=3×10^8 ×t / 0.1

t=5×10^-10 s

Answer 2

Answer:

The answer to this question is Option (D) 5 × 10 -10 s

Explanation:

To Answer this question let us have a brief look at the concept involved in this question.

CONCEPT:

Here The main concept is Refraction of light.

When a ray of light travels in vacuum, It travels with the speed of light i.e. 3×10⁸ m/sec. But when a ray of light passes through a medium(let's say a glass slab), Then it bends from it's original path either towards the original path or away from it . This phenomenon of bending of light when it travels from one medium to another is known as Refraction of light.

SOLUTION:

So coming back to the question, Here light travels through a glass slab and we need to find time taken to travel through this medium.

GIVEN: thickness d=10cm=10×10(^-2)=0.1m

Refractive index n=1.5,c= 3 × 10 8 m/s, time t=?

Mathematically, n= Speed of light in vacuum/speed of light in medium given

i.e. n=c/v

As velocity=Distance travelled/Time taken

⇒v=d/t

⇒n=(c×t)/d

⇒(n×d)/c= t

⇒(1.5×0.1)/(3×10⁸)=t

⇒5×10^-10 sec

Hence the answer is option (D) 5×10^-10 sec