Edexcel IGCSEPhysicsGeneral Applications10 Marks
A student investigates radioactive decay.
- (a)The student measures the count rate from a radioactive source over a period of time. She records her results in a table. [Table shows time in minutes and count rate in counts/minute.] (i) Plot a graph of these results on the grid.[3]
- (a)(ii)Draw the curve of best fit.[1]
- (a)(iii)Use your graph to determine the half-life of the radioactive source.[3]
- (b)Explain why the activity of a radioactive source is measured in becquerels (Bq).[1]
- (c)Explain why radioactive sources should be handled carefully.[2]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme. The mark or mark type is shown in brackets.
- Question 18(a)(i)
- suitable scale chosen for x-axis (1)
- suitable scale chosen for y-axis (1)
- all points plotted correctly (± half a square) (1)
- MP1 for labelling the axes (Time/minutes and Count rate/counts per minute) with correct units (no mark awarded for simply transcribing the column headings) (no mark for just plotting points)
- MP2 for choosing a suitable scale so points cover at least half of the grid in each direction
- MP3 for plotting points correctly (all points to ± half square)
- Question 18(a)(ii)
- smooth curve of best fit (1)
- Question 18(a)(iii)
- initial count rate identified (1)
- half-value identified (1)
- half-life read from graph (1)
- e.g. 500 counts/min at 0 minutes, so half-value is 250 counts/min. Reading this from the graph gives half-life approx 20 minutes.
- Accept value between 19 and 21 minutes
- Question 18(b)
- 1 Bq is 1 decay / disintegration per second (1)
- OR 1 Bq represents the number of nuclei decaying per second
- Question 18(c)
- radiation is ionising (1)
- can cause cell / tissue damage (1)
- OR can cause mutations / cancer / death
- Allow radiation can damage DNA
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