Question

4. Light travels from air into glass slab of thickness 50 cm and refractive index 1.5.

(a) What is the speed of light in glass?

(b) What is the time taken by the light to travel through the glass slab?

(c) What is the optical path of the glass slab?

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Answer 1

Answer:

speed of light in glass is 2 into 10 power 8 metre per second

approx 30 second time will be taken to travel a 1 metre glass slab

when light enters from air into the glass it refract away from the normal and when it enters again from glass to air it reflects towards the normal

Answer 2

Answer:

According to our calculations :

1) speed of light = 2 x $10^8 ms^-1$

2) Total time taken by the light to travel through slab = 2.5 x  $10^-^7 s$

3) Optical path = 75cm

Explanation:

According to the question, given information is given to us :

• Glass slab’s thickness, denoted by d = 50 cm = 0.5m

• Refractive index, denoted by n = 1.5

And we know that refractive index, n is given by the formula : n = c/v

(i) speed of light in glass can be calculated as follows:

V = c/n

= (3 x $10^8$) / 1.5

= 2 x $10^8$ $ms^-^1$

(ii) Total time taken by the light to travel through slab is :

t = d/v

t = 0.5 / (2 x $10^8$)

= 2.5 x $10^-^7$ s

(iii) Optical path can be calculated as follows :

d = nd = 1.5 x 0.5

= 0.75m

= 75cm

If there had been a glass slab, light would have travelled 25 cm farther (75 cm - 50 cm) by the same time.

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