Past Paper Corrections

Question 1

How could a teacher find out if the results are reproducible?

Answer 1

Get other groups or different people (e.g. students) to carry out the experiment

Question 2

Explain how, when light of a star passes through an exoplanet’s atmosphere, an absorption spectrum arises and is used to identify gases in its atmosphere (3)

Answer 2

• An absorption spectrum arises because gases absorb some light
• different gases (or elements) absorb light at different wavelengths
• so a different pattern of black lines is produced

Question 3

State Newton’s first law of motion

Answer 3

If there is zero resultant force on an object, it moves at a constant velocity or is stationary.

Question 4

Why would a teacher choose a large number of dice to model radioactive decay? (2)

Answer 4

Radioactive decay (and dice throwing) is a random process. A larger number reduces the effect of random variations.

Question 6

A teacher adds blue cubes to her dice throwing model of radioactive decay, that will not be removed. What physical quantity do the blue cubes represent?

Answer 6

A non-radioactive material present

Question 7

A scientist works with something that decays by beta and gamma emission. Why, for his own safety, does he store it ina lead box? (3)

Answer 7

1) lead blocks all the beta radiation emitted
2) lead reduces the gammas radiation emissions
3) this reduces the exposure and harm to the scientist

Question 8

Describe and compare controlled nuclear fission and nuclear fusion reactions (6 QER) (10)<— this would cover more than enough

Answer 8

• nuclear fission is when a heavy nucleus (e.g. U-235) absorbs a slow neutron and splits into lighter nuclei, releasing energy and excess neutrons.
• The fission reaction can be controlled safely with boron rods that absorb excess neutrons.
• A moderator is needed to slow down the neutrons so they can cause further fission events, in a chain reaction
• In nuclear fission, two lighter nuclei (e.g. deuterium), collide and fuse, producing helium and releasing energy.
• The process requires very high temperature and pressure, making it very difficult to maintain
• nuclear fission is the splitting of nuclei, fusion is the joining of nuclei
• Currently, fission is used energy generation but fusion reactors have not yet been built.
• Badly-controlled fusion reactors can overheat and cause meltdown. While fusion reactors will be much safer and shut down automatically
• fission products are long half-life, radioactive materials and require safe storage. While, fusion does not produce long half-life radioactive waste
• Per kilogram, fusion releases more energy than fission