Modern Physics 5 Question 22

25. Let mp be the mass of proton, mn the mass of neutron. M1 the mass of 1020Ne nucleus and M2 the mass of 2040Ca nucleus. Then

(1998,2M)

(a) M2=2M1

(b) M2>2M1

(c) M2<2M1

(d) M1<10(mn+mp)

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Answer:

Correct Answer: 25. 9

Solution:

  1. Due to mass defect (which is finally responsible for the binding energy of the nucleus), mass of a nucleus is always less than the sum of masses of its constituent particles.

1020Ne is made up of 10 protons plus 10 neutrons. Therefore, mass of 1020 Ne nucleus, M1<10(mp+mn).

Also, heavier the nucleus, more is the mass defect.

Thus, 20(mn+mp)M2>10(mp+mn)M1

 or 10(mp+mn)>M2M1 or M2<M1+10(mp+mn) Now since M1<10(mp+mn)M2<2M1



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