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Nuclear Fission and Fusion: Quiz

Seven questions on mass defect, binding energy, fission, fusion, chain reactions and reactors, with explanations.

7 questionsIntermediate

7 questions

  1. Question 1EasyThe mass of a nucleus compared with the total mass of its separate protons and neutrons is:
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    Answer: smaller

    The difference is the mass defect, released as binding energy (E = Δm c²) when the nucleus formed.

  2. Question 2MediumComplete: ¹₀n + ²³⁵₉₂U → ¹⁴¹₅₆Ba + ⁹²₃₆Kr + ?
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    Answer: 3 ¹₀n

    Mass numbers: 1 + 235 = 236 = 141 + 92 + 3. Atomic numbers: 92 = 56 + 36 + 0. So three neutrons.

  3. Question 3EasyWhich nucleus has the highest binding energy per nucleon?
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    Answer: ⁵⁶Fe

    Iron-56 lies near the peak of the curve (about 8.8 MeV per nucleon); uranium-235 is about 7.6 and helium-4 about 7.1.

  4. Question 4EasyWhat is the job of the control rods in a nuclear reactor?
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    Answer: to absorb neutrons and control the rate of fission

    Control rods (boron, cadmium) absorb neutrons. The moderator slows them; the coolant carries the heat.

  5. Question 5MediumWhy does fusion require temperatures of millions of degrees?
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    Answer: to overcome the repulsion between positively charged nuclei

    Nuclei are positive and repel each other; only very fast collisions bring them close enough for the strong force to join them.

  6. Question 6MediumHow much energy is released when 1.00 × 10⁻³ kg of mass is converted completely (c = 2.998 × 10⁸ m/s)?
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    Answer: 8.99 × 10¹³ J

    E = mc² = (1.00 × 10⁻³ kg)(2.998 × 10⁸ m/s)² = 8.99 × 10¹³ kg m²/s² = 8.99 × 10¹³ J.

  7. Question 7HardA mass defect of 0.0300 u corresponds to how much energy? (1 u = 931.5 MeV)
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    Answer: 27.9 MeV

    0.0300 u × 931.5 MeV/u = 27.9 MeV.