CBSE Class 10 Science 2015 Term II Outside Delhi Set 1

© examsnet.com
Question : 4
Total: 36
The absolute refractive indices of glass and water are 43 and 32 respectively. If the speed of light in glass is 2×108m s, calculate the speed of light in (i) vacuum, (ii) water.
Solution:  
(i) Given: ng=
4
3
,nw=
3
2
,vg=2×108m s

We know that for glass,
ng=
c
vg

Speed of light in air or vacuum,
c=ngvg
=
4
3
×2
×108
=2.67×108m s

(ii) Also in water,
nw=
c
vw

vw=
c
nw
=
2.67×2×108
3

Speed of light in water =1.78×108m s.
© examsnet.com
Go to Question: