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10 Fusion and fission are nuclear reactions in which large amounts of energy are released - Edexcel - GCSE Physics - Question 10 - 2018 - Paper 1
Question 10
10 Fusion and fission are nuclear reactions in which large amounts of energy are released. a) (i) In a fusion reaction, two hydrogen nuclei are forced together to f... show full transcript
Worked Solution & Example Answer:10 Fusion and fission are nuclear reactions in which large amounts of energy are released - Edexcel - GCSE Physics - Question 10 - 2018 - Paper 1
Step 1
Explain why a very high temperature is needed for this reaction to happen.
Answer
In order for fusion to occur, hydrogen nuclei must overcome the electrostatic repulsion between them, as both nuclei carry a positive charge. At very high temperatures, particles have high kinetic energy, which increases the likelihood of collisions between the hydrogen nuclei. This high kinetic energy allows the nuclei to come close enough for the strong nuclear force to take effect, enabling them to fuse into a helium nucleus.
Step 2
Calculate the decrease in mass.
Answer
To calculate the decrease in mass, use the equation:
Given that the energy released in one fusion reaction is 4.5 x 10^{-12} J and the speed of light is 3.0 x 10^8 m/s, we rearrange the equation to find m:
m = rac{E}{c^2}
Substituting the given values:
m = rac{4.5 imes 10^{-12}}{(3.0 imes 10^{8})^2}
m = rac{4.5 imes 10^{-12}}{9.0 imes 10^{16}}
.
Step 3
Explain how the graphite core and the movable rods are used to maintain and control the chain reaction.
Answer
The graphite core serves as a moderator in the nuclear reactor. It slows down the neutrons produced during fission, allowing them to be more effectively captured by fissile material, leading to a sustained chain reaction.
Movable control rods are made of materials that absorb neutrons, such as boron or cadmium. By adjusting the position of these rods, operators can control the rate of the chain reaction; inserting rods further into the reactor absorbs more neutrons, decreasing the reaction rate, while withdrawing them allows for more neutrons to propagate the fission process. This balance maintains safe operation and ensures a steady supply of energy.