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CBSE · Class 12 · Physics

Nuclei

Standard difficulty · 20 questions · 40 marks

Name: Date: Score: ____ / 40

Show your working for Sections B and C. Answers are on the last page — try every question first!

Section A — Choose the correct answer8 × 1 = 8 marks
1.
The radius of a nucleus of mass number 1 is: (R0 = 1.2 fm)
  1. 0.6 fm
  2. 2.4 fm
  3. 2.2 fm
  4. 1.2 fm
2.
The ratio of the radii of nuclei of mass numbers 216 and 125 is:
  1. 216 : 125
  2. 5 : 6
  3. 6 : 5
  4. 46656 : 15625
3.
The mass defect of a nucleus is 0.01422 u. Its binding energy is: (1 u = 931.5 MeV)
  1. 6.62 MeV
  2. 0.13 MeV
  3. 132.46 MeV
  4. 13.25 MeV
4.
The binding energy of 6027Co is 420 MeV. Its binding energy per nucleon is:
  1. 7 MeV
  2. 15.56 MeV
  3. 12.73 MeV
  4. 14 MeV
5.
Nuclei with the same atomic number but different mass numbers are called:
  1. isotopes
  2. isotones
  3. isomers
  4. isobars
6.
The nucleus 42He contains:
  1. 3 protons and 2 neutrons
  2. 2 protons and 2 neutrons
  3. 2 protons and 4 neutrons
  4. 4 protons and 2 neutrons
7.
The nuclei 168O and 2311Na are:
  1. isotones
  2. isotopes
  3. none of these
  4. isobars
8.
Assertion (A): Nuclei of mass numbers 64 and 125 have the same nuclear density.
Reason (R): The nuclear force is short-ranged and charge-independent.
  1. Both A and R are true, and R is the correct explanation of A.
  2. Both A and R are true, but R is not the correct explanation of A.
  3. A is true, but R is false.
  4. A is false, but R is true.
Section B — Short answer8 × 2 = 16 marks
9.
The mass of the 4020Ca nucleus is 39.9874 u. Find its mass defect, binding energy and binding energy per nucleon. (m_p = 1.00728 u, m_n = 1.00867 u, 1 u = 931.5 MeV)
10.
How much energy is equivalent to 1 g of mass? How many kWh is that? (c = 3 × 108 m/s)
11.
A reactor produces 600 MW, and each fission of U-235 releases 200 MeV. How many fissions take place each second? (1 MeV = 1.6 × 10−13 J)
12.
U-236 (binding energy 7.6 MeV per nucleon) splits into two nuclei of mass numbers 117 and 119, each with 8.6 MeV per nucleon. Estimate the energy released.
13.
Two deuterons (21H, 1.11 MeV per nucleon) fuse to form a helium nucleus (42He, 7.07 MeV per nucleon). Find the energy released.
14.
A nucleus has 4 times the radius of a nucleus of mass number 4. Find its mass number, and compare the densities of the two.
15.
How many nuclei are there in 18 g of cobalt-60? How many neutrons do they contain in all? (N_A = 6 × 1023 per mol)
16.
Write the number of protons, neutrons and nucleons in 168O, and name one isotope of it.
Section C — Word problems4 × 4 = 16 marks
17.
Find the binding energy and binding energy per nucleon of 147N, whose nuclear mass is 13.98859 u. Is it more or less tightly bound than 56Fe (8.8 MeV per nucleon)? (m_p = 1.00728 u, m_n = 1.00867 u, 1 u = 931.5 MeV)
18.
A nuclear power station makes 1000 MW of power from U-235 at 25% efficiency. Each fission releases 200 MeV. Find the number of fissions per second and the mass of U-235 used in one day. (1 MeV = 1.6 × 10−13 J, N_A = 6 × 1023 per mol)
19.
In a fission, U-236 (7.7 MeV per nucleon) splits into two middle-sized nuclei of about 8.6 MeV per nucleon. Estimate the energy per fission, and the energy from the fission of 5 g of U-235 in joules. (N_A = 6 × 1023 per mol, 1 MeV = 1.6 × 10−13 J)
20.
Find the radii of nuclei with mass numbers 64 and 125, the ratio of their volumes, and show that their densities are equal. (R0 = 1.2 fm)
AmbifulWorksheets
Practice that never repeats
CBSE · Class 12 · Physics

Answer key

Nuclei · AW-12P-NUC-2026-V1 · For parents — fold back or tear off before handing the sheet to your child.

QAnswerWorking
1(d) 1.2 fmR = R0A^(1/3) = 1.2 × 1
2(c) 6 : 5R ∝ A^(1/3)
3(d) 13.25 MeVBE = Δm × 931.5 MeV
4(a) 7 MeV420 ÷ 60
5(a) isotopes—
6(b) 2 protons and 2 neutronsneutrons = A − Z
7(c) none of thesenothing in common
8(b) Both A and R are true, but R is not the correct explanation of A.A is true: R3 ∝ A, so mass/volume does not depend on A. R is true but does not explain A.
9Δm = 0.3316 u; BE = 308.89 MeV; 7.72 MeV per nucleonΔm = 20 × 1.00728 + 20 × 1.00867 − M
109 × 1013 J; 2.5 × 106 kWhE = mc2 = 1 × 10−3 × 9 × 1016; 1 kWh = 3.6 × 106 J
111.875 × 1019200 MeV = 3.2 × 10−11 J; n = 600 × 106 ÷ (3.2 × 10−11)
12236 MeV236 × (8.6 − 7.6)
1323.84 MeV4 × 7.07 − 2 × (2 × 1.11)
14A = 256; the densities are equalR ∝ A^(1/3), so A grows 43 = 64 times
151.8 × 1023 nuclei; 5.94 × 1024 neutrons18/60 mol × 6 × 1023; 33 neutrons each
168 protons, 8 neutrons, 16 nucleons; any oxygen nucleus with a different mass numberA = Z + N
17Δm = 0.12306 u; BE = 114.63 MeV; 8.19 MeV per nucleon; less tightly boundBE = [Zm_p + Nm_n − M] × 931.5
181.25 × 1020 per second; 4,230 g a dayheat needed = 4 × electrical power; mass = n × 86,400 × 235/N_A
19212.4 MeV; 4.34 × 1011 Jnuclei in 5 g = 5/235 × 6 × 1023
204.8 fm and 6 fm; volumes 64 : 125; mass is also in that ratio, so density is the sameV ∝ R3 ∝ A