# Significance of Surface and Coulomb Terms

1. Nov 14, 2007

### genloz

I recently had a test question posed to me that asked firstly for an explanation of the terms in the semi empircal mass forumla (which I gave correctly) but then went on to ask:

For
$$^{40}_{20}Ca$$
and
$$^{208}_{96}Pb$$
estimate the fraction of the binding energy provided by the surface and coulomb terms, and comment on the significance of these results...

So I estimated:
Pb
Surface: 17.23*(208)^(2/3) = 604.868
Coulomb: (0.714*96^2)/(208^(1/3)) = 1110.58

Ca
Surface: 17.23*(40)^(2/3) = 201.52
Coulomb: (0.714*20^2)/(40^(1/3)) = 83.5

But could not work out at all what the significance was... I have a feeling the same question will be on the exam, so I was wondering if anyone could give me a clue please?

2. Nov 16, 2007

### genloz

Well I've found that for higher atomic numbers the surface and coulomb terms are almost equal to the binding energy, but they're subtracted from the volume term which makes me confused again...

3. Nov 16, 2007

### genloz

Also how do I estimate total binding energy without the other terms?