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GCSE Physics - Nuclear Fission & Fusion - Help

Doing AQA GCSE Physics. In the specification, it says candidates should know a couple of things, that I don't know the answer to myself:

Explain why the early Universe contained only hydrogen but now contains a large variety of different elements.
Explain how stars are able to maintain their energy output for millions of years.

Thanks
Reply 1
Avatar for DJon
DJon
1
I suggest you take a look at these videos, they're really helpful:

http://www.youtube.com/watch?v=mmF7qZn3jU4&index=14&list=PLv1VZUVRC2VjhLN8K1nU_-2KOdKIbbZqf

http://www.youtube.com/watch?v=diWrXeP6H88&list=PLv1VZUVRC2VjhLN8K1nU_-2KOdKIbbZqf&index=15

Hope that helps a bit!
Reply 2
Avatar for Parallex
Parallex
6
1) The early Universe only contained Hydrogen, fusion created Helium. In stars, Helium is produced from the fusion of Hydrogen and this will take place for a few billion years. When the star begins to run out of hydrogen, it expands to form a Red Giant, which then condenses into a white dwarf (where the temperatures are now very high) so the other (lighter) elements can now be created from the fusion of Helium. Depending on the size of the star, if it is a massive star then it can explode into a supernova and create many, many other elements due to the temperature (and amount of energy) that it reaches in that very short amount of time.

2) The size of stars (and hence the amount of Hydrogen that they contain) is mainly the reason for how they are able to maintain their energy output. The amount of Hydrogen that is fused is a very, very, very small amount in comparison to the total amount of hydrogen. Also, our Sun (and other Main Sequence Stars) are not hot enough for fusion to take place, so a rare event called Quantum Tunneling takes place to form the Helium. Quantum tunneling is rare but because of the sheer size of the Sun, this happens regularly to atoms and therefore a lot of energy is produced per second.
Original post by tmifan
Doing AQA GCSE Physics. In the specification, it says candidates should know a couple of things, that I don't know the answer to myself:

Explain why the early Universe contained only hydrogen but now contains a large variety of different elements.
Explain how stars are able to maintain their energy output for millions of years.

Thanks


Can you provide a link to the specification pls

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