Okay so my book says (the context is electron hydrogen energy levels) the probability of finding the electron within dv=dv(r,∅,θ) is : ψψ*r^2sinθdθd∅  where ψ is the wavefunction And to find within dr of r is : ∫∫ψψ*r^2sinθdrdθd∅, where the inner integral ranges over 0 to PI and the outter from 0 to 2PI I don't really understand this. Why doesn't the first integral  for dv not require dr? As isnt the volume element given by r^2sinθdrdθd∅? I also dont really understand why we don't need to include some integral limits corresponding to dr in  If anyone can help explain things this would be greatly appreciated . Ta in advance !!