(a) Find the refractive index of glass with respect to water. Given : `mu_(gw)=(3)/(2) "and" mu_(w)=(4)/(3)`.
(b) A source of yellow light placed in air is observed by a person swimming under water. If the wavelength of yellow light in air is `6000 Å`, then find its speed, wavelength and colour as observed by the person.

Explanation

(a) `mu_(gw)=(mu_(g))/(mu_(w))=(3)/(2) div (4)/(3)=(3)/(2)xx(3)/(4)=(9)/(8)`
(b) `mu_(w)=(c)/(c_(w))`
or `c_(w)=(c)/(mu_(w))=(3xx10^(8)m//s)/(4//3)impliesc_(w)=(9)/(4)xx10^(8)m//s`
or `c_(w)=2.25xx10^(8)m//s`
Now, `mu_(w)*lambda_(w)=lambda"or" lambda_(w)=(lambda)/(mu_(w))=(6000Å)/(4//3)=(6000xx3)/(4)Å`
`implieslambda_(w)=4500Å`.
Colour for the human eye depends on the frequency. Since frequency is independent of the media, the light as seen by the person inside water will be yellow.