(a) 20 000 Hz
Although
this question only asked for the upper limit of human hearing you need to
remember that
the complete range goes from 20 Hz to 20 000 Hz.
(b) Electromagnetic waves
(c) (i) X-rays
are absorbed by metals and if not removed the
jewellery would show up on the X-ray.
When
a question asks you to ‘explain’, the points that you make should be linked. An
alternative to the second point given here would be ‘if the jewellery were not
removed its image could block out important detail’.
(ii) X-rays
are a form of ionising radiation, whereas ultrasound is non-ionising.
Ionising
radiation like X-rays can damage or even kill healthy body cells.
This
question asks for a comparison and so it is important that both X-rays and
ultrasound are mentioned.
(iii) The
images from X-rays are much more detailed.
(d) (i) 800/200 = 4
10000/4 = 2500
so 1 in
2500 3
The
calculation has been clearly set out. It would have been easy to make a slip
and multiply the 10 000 by 4 to end up with an incorrect answer of 1 in
40 000. However, had this been done, hopefully it would have been realised
that this figure suggests a lower risk, whereas the data in the table clearly
indicate a greater risk.
(ii) The
benefit of a CT scan in being able to help diagnose a serious illness is far greater than the
additional risk of developing cancer due to the scan.
The
two points have been clearly linked.
Remember read the mark scheme carefully. Think about the use of the keywords and check that examiner will be able to credit you with full marks for your answer.
No comments:
Post a Comment