HR Diagrams: Space: Edexcel A-level Physics

[@shiveksoni6534]

Hi, could you explain this formula that you wrote: 3/2 KT=Q/4πe0r

[@nutshellphy]

3/2kT is the expression from thermodynamics for the kinetic energy of a particle, in this case, for a proton on approaching another. kQ^2/r (it was Q^2 and not Q?) is the expression for electrical energy, where kQ/r is electric potential. This electrical energy is that energy needed for 2 protons to approach within a distance r of each other. In order to overcome their repulsion. So in order for fusion to occur, the KE of the incoming particle must equal the energy required for what is called 'closest approach'.

[@shiveksoni6534]

@@nutshellphy so it should be Vgrav=Ek. So 3/2KT=KQ/r right?

[@nutshellphy]

But Vgrav is not energy, it’s energy per kg. So you would have to multiply by the mass to make them equivalent. And Vgrav is not kQ/r since that’s the expression for electric potential. But you could construct a chain of equivalence, yes, where gravitational potential energy converts to kinetic which in turn converts to electrical as the protons approach. This is what happens in gravitational collapse during star birth.