# Answer to Question #65373 in Astronomy | Astrophysics for King

Question #65373

The mean free path of photons in stars is of the order of 0.2 cm. Show that the time

taken for a photon to reach the surface of a star of radius 4 Ro is of the order of one

million year.

taken for a photon to reach the surface of a star of radius 4 Ro is of the order of one

million year.

Expert's answer

The time for beam traveling is given by the expression t = (Ro)^2/(l*c) or in our case t = 16*(Ro)^2/(l*c). Thus, t = 16*(6.96*10^8 m)^2/(2*10^-3 m * 3*10^8 m/s) = 412000 years.

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