Unit 10 Fusion in Stars Checkpoint

What is nuclear fusion?

• The splitting of heavy atoms

• The process of atoms losing electrons

• The process where two light atoms combine to form a heavier atom

• None of the above

Answer explanation

Nuclear fusion is the process where two light atoms combine to form a heavier atom, releasing energy. This is different from nuclear fission, which involves the splitting of heavy atoms.

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What are the two main conditions required for fusion to occur in stars?

• Low temperature and high pressure

• High temperature and low pressure

• Low temperature and low pressure

• High temperature and high pressure

Answer explanation

Fusion in stars requires high temperature to provide the energy needed to overcome the electrostatic repulsion between positively charged nuclei, and high pressure to bring them close enough for fusion to occur.

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What element is primarily involved in the fusion process in stars like the Sun?

• Carbon

• Hydrogen

• Oxygen

• Iron

Answer explanation

The fusion process in stars like the Sun primarily involves hydrogen. In the core, hydrogen nuclei combine to form helium, releasing energy that powers the star. Other elements like carbon, oxygen, and iron play roles in later stages of stellar evolution.

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Why is it necessary for a star to have extremely high temperatures and pressures in its core for fusion to occur?

• To overcome the repulsive forces between positively

• To prevent the core from collapsing

• To charged hydrogen nuclei

• To create magnetic fields

Answer explanation

Fusion requires extremely high temperatures and pressures to overcome the repulsive forces between positively charged hydrogen nuclei. This allows them to collide with enough energy to fuse, releasing energy in the process.

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What is the name of the force that allows hydrogen nuclei to overcome their repulsion and fuse together in a star?

• Electromagnetic force

• Strong nuclear force

• Gravitational force

• Weak nuclear force

Answer explanation

The strong nuclear force is the fundamental force that binds protons and neutrons in an atomic nucleus. In stars, it allows hydrogen nuclei to overcome their electromagnetic repulsion and fuse, releasing energy.

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What happens to the mass of products during fusion?

• It stays the same

• It decreases slightly

• It increases significantly

• It is converted into iron

Answer explanation

During fusion, some mass is converted into energy according to Einstein's equation E=mc². This results in a slight decrease in the mass of the products, making 'It decreases slightly' the correct choice.

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What happens after a star runs out of hydrogen in its core?

• The star begins to fuse heavier elements like helium

• The star shrinks to form a black hole

• The star turns into a planet

• The star cools down and stops shining

Answer explanation

After a star exhausts hydrogen in its core, it begins to fuse heavier elements like helium. This process leads to changes in the star's structure and energy output, eventually resulting in different stellar evolution stages.

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Which of the following best describes the role of gravity in a star's fusion process?

• Gravity keeps the star cool and prevents fusion

• Gravity slows down the fusion process

• Gravity compresses the star’s core, creating the necessary pressure for fusion

• Gravity causes fusion by pulling atoms together

Answer explanation

Gravity compresses the star's core, increasing pressure and temperature, which are essential for nuclear fusion to occur. This process allows hydrogen atoms to fuse into helium, releasing energy that powers the star.

What type of energy is released during fusion in stars?

• Electrical energy

• Gravitational energy

• Light and heat

• Chemical energy

Answer explanation

During fusion in stars, hydrogen nuclei combine to form helium, releasing energy primarily in the form of light and heat. This process powers stars and is essential for their luminosity.

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What is the main reason the Sun will eventually stop fusing hydrogen in its core?

• The Sun will run out of hydrogen

• The Sun will become too hot for fusion to continue

• The Sun will be unable to create helium

• The Sun’s gravity will stop the fusion process

Answer explanation

The main reason the Sun will eventually stop fusing hydrogen is that it will run out of hydrogen in its core. Once the hydrogen is depleted, fusion will cease, leading to changes in the Sun's structure and energy output.

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