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Radioactivity

Why fusion needs extreme conditions

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Overview

Electrostatic repulsion between nuclei, why high temperature and pressure let them fuse, conditions in the Sun's core, and why a fusion reactor on Earth is so hard to build and run.

What you need to know

Answer each one before you reveal it.

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Key term

Why does nuclear fusion not happen at everyday temperatures?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Why do two nuclei repel one another as they approach?

    Model answer

    Both are positively charged, so there is an electrostatic force of repulsion between them.

  2. 2

    Why does nuclear fusion not happen at everyday temperatures?

    Model answer

    The nuclei move too slowly to overcome their electrostatic repulsion and get close enough to fuse.

  3. 3

    How does an extremely high temperature make nuclear fusion possible?

    Model answer

    The nuclei move fast enough to overcome the repulsion between them and come close enough to fuse.

  4. 4

    Why is a very high pressure also needed for nuclear fusion?

    Model answer

    It packs the nuclei closer together so that collisions happen often enough.

  5. 5

    Where in the Sun are the conditions right for nuclear fusion?

    Model answer

    In the core, where the temperature and the pressure are both extremely high.

  6. 6

    What causes the enormous pressure in the core of a star?

    Model answer

    The huge weight of the outer layers pressing inwards under gravity.

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