A plate glass window (n = 1.5) has a thickness of 4.5 mm. how long does it take light to pass perpendicularly through the plate?

The solution to this is to use the n = c / v equation

Where:

c is the speed of light: 3x10^8; and

The idea that v = m/s

So plug in the m/s for v in the n = c v equation and you will get:

1.5 = (3 x 10 ^ 8) / ((4.5m) / s))

Therefore, the time should be 2.25 x 10 ^ - 10 seconds.