1. A lens in Lick Observatory\'s 36-inch refracting telescope has a thickness of

Question

1. A lens in Lick Observatory's 36-inch refracting telescope has a thickness of 1.96 inches at its center

and an index of refraction n=1.52. Consider blue light (450 nm) passing through the lens.

(1A) What is the light speed in the lens?

(1B) How long does it take light to travel through this lens at the center?

(1C) Through what thickness of both water and vacuum could light travel in the same amount of time?

(1D) How many wavelengths of the incoming blue light fit across the lens at any instant?

Please show/ explain work. Thanks!

Explanation / Answer

1. speed = c/refractive index = 1.974 * 10^8 m/s

2.t = d/v = 1.96 * 0.0254 / v = 2.522 * 10^-10 s

3.water : speed = c/(4/3) = 3/4c =2.25*10^8 m/s

d = v.t = 0.0567 m = 2.234 inches

vacuum: speed = c

d = c.t = 2.979 inches

4.n = d / wavelength = 110631

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