How much time will sunlight take to pass through the glass window of thickness 4 mm ? `mu` of glass = 1.5.

Explanation

Velocity of sunlight in vacuum or in air,
`c = 3 xx 10^(8) m * s^(-1)`
Thus to cross a thickness in a medium of refractive index `mu`,
`v = ( c )/(mu)`
So to cross a thickness d, the time taken by light, `t = (d)/(v) = (dmu)/(c) = ((4 xx 10^(-3)) xx 1.5)/(3 xx 10^(8))`
`["here" " " d = mm = 4 xx 10^(-3) m]`
` = 2 xx 10^(-11)s`