Energy Released in Fission and Fusion · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Splitting and joining for energy

Science · Matter & Materials · ages 17-18
Name ______________________   Date ____________

  1. What is nuclear fusion?

    • Joining light nuclei into a heavier one
    • Splitting a heavy nucleus in two
    • Burning a chemical fuel

  2. What is nuclear fission?

    • Joining two light nuclei
    • Splitting a heavy nucleus
    • Cooling a hot gas

  3. Fusion needs extreme temperature because the nuclei repel each other electrically.

    Circle one:   True   False

  4. Why does fission suit heavy nuclei?

    • Splitting moves them up toward the peak
    • Splitting makes extra protons appear
    • Heavy nuclei are always colder

  5. How do you find the energy a nuclear reaction releases?

    • Count the neutrons alone
    • Measure the temperature rise only
    • Weigh each side; lost mass times c squared

  6. Two nuclei approach slowly and bounce apart unchanged. What went wrong?

    • Heat made the nuclei heavier
    • Only extreme speeds beat the repulsion
    • Slow nuclei attract too weakly

  7. Two proposed joins: a light pair below iron, and a heavy pair above iron. Which releases energy?

    • The heavy pair
    • Both release equally
    • The light pair

  8. Mia plans a power station fusing iron nuclei. What is wrong with her plan?

    • Iron fusion absorbs energy
    • Iron nuclei cannot be heated
    • Iron nuclei have no charge
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Splitting and joining for energy W1-mt_VrqLAATXQY-s1

  1. Joining light nuclei into a heavier one · Fusion joins light nuclei, and the merged nucleus binds tighter.
  2. Splitting a heavy nucleus · Fission breaks one heavy nucleus into lighter fragments, freeing energy.
  3. True · Like charges push apart, so only violent speeds bring nuclei within grabbing range.
  4. Splitting moves them up toward the peak · Heavy nuclei sit below the peak, so splitting climbs toward iron and pays out.
  5. Weigh each side; lost mass times c squared · The mass books must balance, and the missing mass is the payout.
  6. Only extreme speeds beat the repulsion · Gentle speeds never cross the repulsion gap to reach the short range attraction.
  7. The light pair · Only the light join climbs toward the peak, and only climbing pays.
  8. Iron fusion absorbs energy · Iron already crowns the curve, so joining past it slides downhill and costs energy.
Worksheet · LightMySky