Question

color of wavelength in air is 6000 A, and in water it is 4500 A

then what is the speed of light in meters/sec  in water ?

Answer 1

u=c/v Also, u= (lambda)/ lambda'

therefore c/v= lambda/lambda'

v/c=lambda'/ lambda

Hence v=(lambda'/lambda) x c

v=4500/6000 x 3 x 10^8 m/s

v= 2.25 x 10^8m/s

Answer 2

We have a relation, $\frac{Velocity_{medium-1}}{Velocity_{medium-2}}=\frac{Wavelength_{medium-1}}{Wavelength_{medium-2}}$→ Snell's Law.

From this, $Velocity_{water}}=(Velocity_{air})\frac{Wavelength_{water}}{Wavelength_{air}}$

Substitute them, you get $Velocity_{water}}=(2.25)10^{8} m/s$