One to two mark questions will start with command words such as 'describe' or 'explain'. Some command words are easy to understand such as:
The command words 'describe' and 'explain' can be confusing. If you are asked to describe a graph, you will be expected to write about its overall shape, whether it is linear or curved, the slope of gradients etc. If you are asked to explain why a pattern or trend is seen in a graph, you will be expected to use your science knowledge, not just say what you see (which is a description), eg 'The graph shows a steep linear increase for the first three hours because…'.
'Explain how' and 'why' questions often have the word 'because' in their answer. 'Describe' questions don't.
The number of marks per question part is given in the form '[2 marks]'. It is essential that you give two different answers if a question is worth two marks. Sometimes you can gain a second mark by giving the units in a calculation or stating specific data points, eg 'the speed of the object decreased by 8 m/s'.
Edexcel questions courtesy of Pearson Education Ltd.
The figure below shows the structure of an oxygen-14 atom:
State the overall charge of the oxygen-14 atom. [1 mark]
There are eight protons and eight electrons, so the overall charge is zero .
Atoms are always neutral - they have zero overall charge.
A teacher uses a Geiger-Müller tube and a counter to measure background radiation. The reading on the counter tube is 34 counts per minute.
The teacher puts a source of beta radiation 15 cm in front of the same Geiger-Müller tube. The reading on the counter tube is now 468 counts per minute.
a) Calculate how much radiation detected by the Geiger-Müller tube comes from the source of beta radiation. [1 mark]
The teacher puts a thick sheet of aluminium between the source of beta radiation and the Geiger-Müller tube.
b) Estimate the reading on the counter tube. [1 mark]
a) Always subtract the background count to find the extra counts from the source of beta radiation used.
Calculate: 468 - 34 = 434 counts per minute .
b)A thick sheet of aluminium blocks beta particles, so no radiation from the source should reach the Geiger-Müller tube. Only background radiation will reach the detector so the answer should be 34 counts per minute .
State what is meant by the term 'half-life'. [1 mark]
The time taken for the activity of a radioactive nuclide to halve .
The nucleus of americium-238 can absorb an electron.
When this happens, one of the protons in the nucleus becomes a neutron, as shown below.
Describe how absorbing an electron affects the proton number and the nucleon number of a nucleus. [2 marks]
The proton number decreases by 1 . The nucleon number stays the same .
The question has asked for two different things. Make sure you give an answer to both.