The interior of the sun is opaque to light because it is hot enough to ionize the gas in it and photons are strongly scattered by interacting with the free electrons this produces. c) using the fact that the photons travel at the speed of light between collisions, 3 marks d) assuming that the direction of a photon after a collision is independent of its direc- the mean free path of photons in the sun is d. calculate nt), the mean number of collisions that take place in time t. tion before the collision, after a large number of collisions, n, what are i) the average displacement from its starting point, and ii) the root-mean-square distance from its starting point? 5 marks e) for a photon created by a nuclear reaction at the centre of the sun, with d 1mm, calculate how much time is needed before the root-mean-square distance is equal to 5 marks how do we know that nuclear reactions are currently taking place in the centre of 2 marks] the radius of the sun, r= 6.96 × 108 m. the sun?