lecture14_08 - Lecture 14 Energy Generation in the Sun

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Lecture 14 Energy Generation in the Sun We saw that thermal contraction is insufficient to  power the Sun for more than 30 million years. Can nuclear reactions do it? Remember, Celilia  Payne had shown the Sun was nearly entirely  made up of hydrogen and helium. ..  What happens if we compare H and He nuclei ?
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NOT  TO SCALE (An H atom is just a proton in the nucleus, with one electron orbiting it.)
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                                    Solar Nuclear Reactions  1. An atom’s nucleus is composed of  protons   (massive, positively charged particles) and  neutron (massive nuclear particles with no  electric charge). The nuclear particles are held  together by the  strong nuclear force,   which  overcomes the repulsive electrical forces . 2. Nuclear reactions involve the strong forces  between nuclear particles. The strong force is  effective at much  shorter distances  than the  electrical force.
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3. In  nuclear fusion , two nuclei combine to form  a larger nucleus, releasing energy in the  process. In the Sun, 4 hydrogen nuclei are  fused to form 1 helium nucleus and energy.                Mass of 4  H nuclei      =     6.691 x 10 -27   kg              Mass of  1 He nucleus =     6.645 x 10 -27  kg                                            Difference               =     0.046 x 10 -27  kg
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Simplified Proton-Proton Chain (Not all branch reactions shown)
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Clicker Question    (DISCUSS WITH YOUR NEIGHBOURS!) To begin nuclear fusion in a star, high  temperatures are required to overcome: A) nuclear force between the protons B) nuclear force between electrons C) electrical force between the neutrons D) electrical force between the protons
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VOTING
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CORRECT ANSWER: D)  ELECTRICAL FORCE BETWEEN PROTONS
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The temperature has to be high enough for reactions to take place.
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                                Solar Nuclear Reactions (cont.) 4. The fusion process in the Sun converts only 0.7% of  the original mass into energy. ( E = m c  : energy  released) 5. To produce the Sun’s energy output, nearly 5 million  metric tons of matter must be converted into energy  each second. This,in turn, requires 626 billion kg of  hydrogen be transformed into 622 billion kg of helium. 6. The   proton-proton chain  is the series of nuclear  reactions that begins with 4 protons and ends with a  helium nucleus. This chain is the main fusion process  in the Sun, responsible for  98.5%  of the energy  production.
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                      Solar Nuclear Reactions (cont.) 7.
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lecture14_08 - Lecture 14 Energy Generation in the Sun

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