Physics SB1 - SB6

Question 1

Describe the process of nuclear fission.

Answer 1

1. In a nuclear reactor, a slow-moving neutron is absorbed into a nucleus ( typically uranium 235 ). This causes the nucleus to become uranium 236 which is unstable.

2. The entire nucleus splits into 2 large fragments called ‘daughter nuclei’. 2-3 neutrons also explode out of the fission reaction that go on to collide with other nuclei, causing a chain reaction.

3. The fast moving neutrons carry most of the energy from the reaction with them but before the neutrons can collide with fresh uranium nuclei, they need to be slowed down.

4. Their energy is passed on to other components in the nuclear reactor, which is used to heat water to drive the turbines that turn the generators.

Question 2

Describe the function of each part of a nuclear reactor.

Answer 2

1. Morderator - a graphite core, for example, slows the neutrons down so that they are more likely to be absorbed into a nearby fuel rod.

2. Control Rods - these are raised and lowered to stop neutrons from travelling between fuel rods and therefore change the speed of the chain reaction.

3. Coolant - this is heated up by the energy released from the fission reactions and is used to boil water to drive turbines in the power stations.

4. Concrete Shield - the daughter products of the fission reaction are radioactive and can be a hazard.

Question 3

What are some disadvantages & advantages of using Nuclear Power Stations.

Answer 3

1. Advantages:

• Produces no polluting gases.
• Power station has very long lifetime.
• Very low fuel costs.

2. Disadvantages:

• Waste is radioactive and safe disposal is very difficult and expensive.
• Large-scale accidents can be catastrophic.
• Costs of building and safely decommissioning are very high.

Question 4

What are some advatanges & disadvantages of using irratdation.

Answer 4

Advantages:

1. Sterilisation can be done without high temperatures.

2. It can be used to kill bacteria on things that would melt.

Disadvantages:

1. It may not kill all bacteria on an object.

2. It can be very harmful - standing in the environment where objects are being treated by irradiation could expose people’s cells to damage and mutate.

Question 5

What are some advantages & disadvantages of Contamination?

Answer 5

Advantages:

1. Radioactive isotopes can be used as medical and industrial tracers

2. Use of isotopes with a short half-life means exposure can be limited

Disadvantages:

1. Radioactive isotopes may not go where they are wanted

2. It can be difficult to ensure that the contamination is fully removed so small amounts of radioisotope may still be left behind.

Question 6

What is some evidence to support the Big Bang Theory?

Answer 6

1. Red Shift

• It has been discovered that the** further away a galaxy** is, the more red shifted it’s light is. Meaning, the further away the galaxy is, the faster they are moving.
• Which is similar to an explosion when the fastest travelling parts move away the furtherst.
• Providing evidence the universe itself is expanding.

2. CMBR

• CMBR is the remains of the thermal energy from the Big Bang, spread thinly across the whole Universe.
• This comes from all directions in space and has a temperature of about -270°C.

Question 7

Describe the Life Cycle of Stars ( Include different routes )

Answer 7

1. Nebula - A star forms from massive clouds of dust and gas in space. Mostly composed of hydrogen.

Gravity then pulls the dust and gas together

2. Protostar - As the mass falls together it gets hot. A star is formed when it is hot enough for the hydrogen nuclei to fuse together to make helium.

3. Main Sequence Star - The force of gravity holding the star together is balanced by higher pressure due to the high temperatures.

4. Red Giant Star - When all the hydrogen has been used up in the fusion process, larger nuclei begin to form and the star may expand to become a red giant.

5. White Dwarf - When all the nuclear reactions are over, a small star like the Sun may begin to contract under the pull of gravity. This fades and changes colour as it fades.

6. Black Dwarf

7. Supernova - A larger star with more mass will go on making nuclear reactions, getting hotter and expanding until it explodes as a supernova.

8. Black Hole/Neutron Star - Depending on the mass at the start of its life, a supernova will leave behind either a neutron star or a black hole.