Cambridge International AS Level Physics
Answers to end-of-chapter questions
Answers to EOC questions
■■
Chapter P1
1
2
3
a 25.8 ± 3.3 cm or better 26 ± 3 cm
b 2.80 ± 0.18 cm or better 2.8 ± 0.2 cm
c 24.0 ± 0.1 g
[1]
[1]
[1]
a 1.1 ± 0.1 V; 0.7 ± 0.1 V
[1]
b If R = kl then the two values of k are
0.0440 Ω cm–1 and 0.0467 Ω cm–1.
[1]
The criterion is that, if the resistance is
proportional to length, then the percentage
diference in the values of k is less than the
percentage uncertainty in the value of V. [1]
Percentage diference in k values
0.27 = 0.6%
= 0.044
[1]
Percentage uncertainty in lowest value of
V is 14%, so the data is consistent with R
proportional to l.
[1]
Apart from taking only two readings, which is
not enough, it is dificult to:
■■ release the ball without giving it an initial
velocity
[1]
■■ start the stopwatch as the ball is released
[1]
■■ stop the stopwatch exactly as the ball
crosses the line
[1]
■■ release the ball exactly on the line
[1]
■■ measure small times that are not much
larger than reaction times
[1]
■■ avoid the balling rolling to the side of the
track
[1]
■■ measure the distance without introducing
parallax error
[1]
Suggested improvements
■■ take readings at about five values of s and
2
■■ plot a graph of T against s
[1]
■■ take a video of the ball rolling down the
ramp with a timer in the background and
play it back frame by frame
[1]
■■ use a metal ball, held to an electromagnet
at the same start position each time,
turning of the magnet to start the ball [1]
■■ use longer distances
[1]
■■ have a groove down the middle of the
track
[1]
always view from directly above the mark
on the track when using a rule
[1]
(Maximum [8] marks: [4] for the problems, and
the other [4] for solutions / improvements.)
4
a Values for m correct and to the same
number of significant figures, or one more
than data
[1]
Values for T correct and to the same number
of significant figures, or one more than data
[1]
Mass / g
0.5
T20 / s
m/g
T/s
20
12.2
4.5
0.610
50
15.0
7.1
0.750
100
18.7
10.0
0.935
150
21.8
12.2
1.090
200
24.5
14.1
1.225
190
24.0
13.8
1.200
1.4
1.2
1.0
0.8
T/s
0.6
0.4
0.2
0.0
0
5
10
15
m / g 0.5
b Sensible axes used and labelled with
quantity and unit
[1]
All points plotted to within half a small square
[1]
All points close to line
[1]
Line of best fit correct
[1]
c Gradient drawn with more than half length of
drawn line; value between 0.062 and 0.064 [1]
y-intercept between 0.30 and 0.32
[1]
d C = value given for y-intercept with unit s,
e.g. 0.31 s
[1]
k = value given for gradient with unit, e.g.
0.063 s g–0.5
[1]
Cambridge International AS and A Level Physics © Cambridge University Press 2014
Cambridge International AS Level Physics
5
a i 127 cm
[1]
ii 3 cm
[1]
2%
[1]
iii 4.7 s
[1]
iv 0.1 s
[1]
2%
[1]
b i When l = 40 cm, v = 27 cm s–1;
when l = 60 cm, v = 38 cm s–1
[1]
ii Two significant figures, as this was the
lower of the number of significant figures
for s (3 sig. figs) and t (2 sig. figs)
[1]
s
c i, ii k = l = 3.175 and 3.167. The percentage
diference in k values is 0.26%.
[1]
This is less than the percentage uncertainty
in s = 2%, so the data is consistent with s
proportional to l.
[1]
d, e See comments for experiment 2, plus
the dificulty of measuring to the middle of
the trolley for l and s (measure from end of
trolley and add on half the length of a trolley
found separately), dificulties that may occur
as the toy car hits the straight section (have
a slightly curved join), and dificulties with
the car not running straight (have wheels in
grooves)
[8]
(Marks: [1] for each sensible source of
uncertainty, to a maximum of [4];
and [1] for each sensible improvement, to a
maximum of [4])
6
a Average value of voltage was 5.9 and
uncertainty is ±0.2 or possibly 0.3 V.
Percentage uncertainty is between 3%
and 5%.
[1]
–2
b i 0.42 °C V
[1]
–2
and 0.35 °C V
[1]
ii Two significant figures, as V was measured
to 2 sig. figs and q was measured to 3 sig.
figs. Choose the lower number.
[1]
iii Percentage diference in values of k is 18%.
This is larger than the 5% uncertainty in
V (which is larger than the percentage
uncertainty in the value of θ). Thus the
data is not consistent with the suggested
relationship.
[1]
Answers to end-of-chapter questions
c Only two voltage readings is not enough. [1]
The voltmeter reading fluctuates because of
contact resistance.
[1]
The voltmeter reading fluctuates because of
a change in mains voltage.
[1]
The voltmeter reading falls because the
resistance of the wire changes as it heats up.
[1]
The temperature increases ater the switch
is turned of (while heat passes from the
resistor to the water).
[1]
(Maximum of [4] marks)
d Clean the wires first.
[1]
Use a car battery.
[1]
Use a metal whose resistance changes little
with temperature.
[1]
Use more than two voltages and plot a graph
of θ against V 2 or calculate more than two
values of k.
[1]
Stir well and take the highest reading on the
thermometer ater switching of.
[1]
(Maximum of [4] marks)
Cambridge International AS and A Level Physics © Cambridge University Press 2014