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Z,A and M represent the atomic number, mass number and rest mass of a nucleus. a. Show that 'M' is always less than the mass of the constituent particles. b. What is this mass difference called ? c. Give the relation. |
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Answer» Solution :a. Protons and neutrons come TOGETHER WITHIN a very SMALL space of the order of `10^(-14)m` to form a nucleus. The energy required to do so is PROVIDED by nucleus at the expense to their masses. Hence the reason. e.g. For `""_5B^(10)`, the mass , `M = 10.012944` `""_(5)B^(10)` consists of 5 protons and 5 neutrons. Hence total mass = `m_P + m_N` `= 5 xx "Proton mass " + 5 xx "Neutron mass"` `= 5 xx 1.007825 + 5 xx 1.008665` `= 5.039125 + 5.043325 = 10.08245 u`. i.e., `M < (m_P + m_N)`, hence the reason. b. This mass difference is called mass defect (`DELTA m)` c. `Deltam = Zm_P + (A - Z) m_N - M`. |
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