A brief note in a physics textbook states that light nuclei must overcome a sizeable electrostatic repulsion before they can fuse.
Answer the following questions with suitable reasoning.
(i) What is meant by the term "Coulomb barrier" with reference to nuclear fusion?
(ii) Using qualitative arguments based on electrostatic potential energy and average thermal kinetic energy, explain why temperatures of the order of 108K are usually quoted as necessary for fusion of deuterium nuclei in laboratory devices.
(iii) The core of the Sun is at a temperature of about 1.5×107K, which is lower than the value mentioned in part (ii). Explain, without using numerical calculations, how fusion of protons is nevertheless possible inside the Sun.