Nuclear Fusion - UNSOLVED PRACTICE SET
Chapter: Nuclei | Topic: Nuclear Fusion
NUCLEAR FUSION - UNSOLVED PRACTICE SET
Topic: Nuclear Fusion
Multiple Choice Questions
Q1. Nuclear fusion is the process in which:
- A heavy nucleus splits into lighter nuclei
- Two light nuclei combine to form a heavier nucleus
- A nucleus emits radiation
- A neutron is captured by a nucleus
Q2. The main fusion reaction in the Sun is:
- Proton-proton chain
- Carbon-nitrogen-oxygen cycle
- Deuterium-tritium reaction
- Uranium fission
Q3. For fusion to occur, the reacting nuclei must have:
- Very low kinetic energy
- Very high kinetic energy to overcome Coulomb repulsion
- Zero kinetic energy
- Equal numbers of protons and neutrons
Q4. The temperature required for thermonuclear fusion is typically:
- 10³ K
- 10⁶ K
- 10⁷ to 10⁸ K
- 10¹² K
Q5. The Lawson criterion refers to:
- The minimum density required for fusion
- The product of plasma density and confinement time required for fusion
- The maximum temperature for fusion
- The energy released per fusion reaction
Q6. Controlled thermonuclear fusion has not yet been achieved on Earth primarily because:
- The reactions do not release energy
- It is extremely difficult to confine plasma at fusion temperatures
- There is insufficient fuel
- The reactions are too slow
Short Answer Questions
Q7. What is nuclear fusion? Write the nuclear equation for the fusion of two deuterium nuclei.
Q8. Why is nuclear fusion difficult to achieve on Earth compared to nuclear fission?
Q9. What is the proton-proton chain? Where does it occur naturally?
Q10. Why does fusion require temperatures of millions of degrees, while fission can occur at room temperature?
Q11. What are the advantages of nuclear fusion over nuclear fission as an energy source?
Q12. What is plasma? Why is it called the fourth state of matter?
Long Answer Questions
Q13. Describe the proton-proton chain reaction that occurs in the Sun. Show the nuclear reactions involved and calculate the net energy released.
Q14. Explain why controlled nuclear fusion is so challenging to achieve. Discuss the problems of plasma confinement, heating, and the Lawson criterion.
Q15. Compare nuclear fission and nuclear fusion as energy sources. Discuss the fuel availability, energy output, radioactive waste, safety, and technological challenges of each.
Numerical & Application-based Problems
Q16. Consider the deuterium-tritium fusion reaction: ²H + ³H → ⁴He + n
(a) Write the balanced nuclear equation.
(b) Calculate the Q-value of this reaction. Given masses: ²H = 2.0141 u, ³H = 3.0160 u, ⁴He = 4.0026 u, n = 1.0087 u.
(c) Calculate the energy released per kilogram of fuel consumed.
(d) Compare this with the energy released per kilogram in the fission of U-235 (about 8 × 10¹³ J/kg).
Q17. The Sun radiates energy at a rate of 3.8 × 10²⁶ W.
(a) Calculate the mass of hydrogen converted to helium per second in the Sun.
(b) Calculate the number of fusion reactions per second if each reaction releases 26.7 MeV.
(c) Estimate how long the Sun can continue to shine at this rate if it contains 10³⁰ kg of hydrogen and only 10% is available for fusion.
Q18. In your school's science exhibition, a student presents a project on fusion energy and India's role.
(a) She explains that ITER (International Thermonuclear Experimental Reactor) in France is a collaborative project including India. The ITER plasma will contain deuterium and tritium at 150 million degrees. Calculate the average kinetic energy of deuterium nuclei at this temperature and compare it with the Coulomb barrier energy between two deuterium nuclei separated by 2 fm.
(b) The student mentions that India's own fusion research is conducted at the Institute for Plasma Research in Gandhinagar. Explain why magnetic confinement (tokamak) is necessary for fusion and why simple material containers cannot hold fusion plasma.
(c) She calculates that if India could achieve controlled fusion, 1 kg of deuterium extracted from seawater could provide energy equivalent to burning 10,000 tonnes of coal. Verify this claim by calculating the energy from 1 kg of deuterium in D-T fusion and comparing with the energy from burning coal (energy density ≈ 30 MJ/kg).
(d) A classmate asks why we don't just use hydrogen bombs (uncontrolled fusion) for peaceful energy production. Explain the fundamental impossibility of this and the difference between uncontrolled and controlled fusion.
(e) India's energy needs are growing rapidly. Discuss how fusion energy, if achieved, could transform India's energy landscape, and what scientific and engineering challenges remain before this becomes reality.