The Sun and Its Ability to Create Power

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Nuclear physics deals with the structure of the nuclei of atoms.

The special theory of relativity deals with the behavior of things moving at close to the speed of light.

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15.2.1 Converting Mass to Energy

Out of the special theory of relativity comes the most famous equation in science:

This equation tells us that mass (m) is just another form of energy (E)!

The c2 is the square of the speed of light.

1 gram of matter is equivalent to the energy obtained by burning 15,000 barrels of oil.

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…but there are rules

We can’t simply convert atoms into energy.

We rearrange the protons and neutrons in nuclei to get a lower-mass configuration.

The difference between initial mass and final mass is converted to energy.

Chemical energy comes from rearranging atoms to configurations of lower energy (mass).

Nuclear energy comes from rearranging nuclei to configurations of lower mass (energy).

In each case, we get out the energy difference.

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Elementary Particles (condensed)

5 particles play a fundamental role in the Sun.

Protons and neutrons make atomic nuclei

Electrons orbit nuclei of atoms

Photons are emitted by the Sun

Neutrinos are also emitted

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15.2.3 The Atomic Nucleus

Two ways to rearrange nuclei and get energy:

Fission

produces energy by breaking up massive nuclei like Uranium into less massive nuclei like Barium and Krypton

A-bombs, nuclear reactors

needs Uranium 235, Plutonium 238

Problem: no Uranium or Plutonium on the Sun

Fusion

produces energy by combining light nuclei like Hydrogen to make more massive nuclei like Helium.

H-bomb, tokamak, internal confinement fusion

Sun has lots of Hydrogen!!

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How Does Fusion Work?

Nuclear fusion:

a process by which two light nuclei combine to form a single larger nucleus.

However: nuclei are positively charged

Like charges repel

Two nuclei naturally repel each other and thus cannot fuse spontaneously

For fusion, electrical repulsion must be “overcome”

When two nuclei are very close the strong nuclear force takes over and holds them together.

How do two nuclei get close enough?

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Fusion needs fast moving nuclei

Fast moving nuclei can overcome the repulsion - they get a running start.