Full Answers to Review Questions - Hodder Plus Home

The overall percentage uncertainty is therefore in the order of 5%
(probably more when also taking into account any manufacturing
tolerance and the mass of the wrapper). This means that the density of
the butter could lie between about 0.95 g cm −3 and 1.03 g cm −3 .
Although the experimental value of 0.98 g cm −3 suggests that butter
will float, the experiment may not be sensitive enough to confirm this
beyond all doubt. (You might like to check what happens with a small
piece of butter in a cup of water!)
2 a) i) For example, mass of packet of paper
M = 2.52 kg
ii) Mass of single sheet
2520 g
m = ______ = 5.04 g
500
b) i) For example:
l/mm 297 297 Average: 297
w/mm 210 210 Average: 210
ii) Area A = 0.297 m × 0.210 m = 0.0624 m 2
5.04 g
‘gsm’ = __________ = 80.8 g m−2
2 0.006 24 m
iii) Percentage difference
= (80.8 – 80) g m−2
_____________________
80 g m−2 × 100% = 1%
Full Answers to Review Questions: 2 A guide to practical work
Table A.2 �
This is acceptable experimental error, particularly when taking into
account the mass of the packet and the lack of sensitivity of the
kitchen scales.
c) i) For example, measured thickness of packet/mm
= 48, 47, 48, 49 ⇒ average = 48 mm
Thickness of single sheet
t =
48 mm
______
500
= 0.096 mm = 0.0096 cm
Density of paper = mass _______
volume
=
5.04 g
_________________________
29.7 cm × 21.0 cm × 0.0096 cm
= 0.84 g cm –3 (840 kg m –3 )
ii) The thickness of a single sheet of paper could be checked as follows:
• First check the micrometer screw gauge or digital callipers for zero
error.
• Fold the paper four times to get 16 thicknesses.
• Compress to remove any air.
• Measure 16 t in four different places.
• Take the average and hence find t.
Tip
Note that your final answer can
be quoted only to the number of
significant figures of the least precise
of your measurements. In this case,
the answer can only be stated to two
significant figures as t has only been
measured to 2 s.f.
Tip
Note the experimental techniques
given here – multiple readings (16 t)
taken in different places – and the
use of bullet points. This is a good
strategy as it helps you set out your
answer in a clear and logical manner.
Examiners love bullet points!
Edexcel Physics for AS © Hodder Education 2009
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