Physics 9702/52 February/March 2019: question paper and mark scheme
Cambridge AS & A Level Physics (9702), Paper 5 Planning, Analysis and Evaluation, February/March 2019. Read both free below, or download them. Done the paper? Get it marked by AI against this mark scheme.
A student is investigating the behaviour of a capacitor-resistor circuit as shown in Fig. 1.1.
R
C input output
Fig. 1.1
A neon lamp flashes on and off when it is connected across the capacitor with a potential difference
VF across the lamp of approximately 90 V.
The student has a number of unmarked resistors.
It is suggested that the period T of the flashes of the lamp is related to the resistance R of the resistor by the expression
T = RCK
where C is the capacitance of the capacitor and K is a constant.
The constant K is given by
Vi – VL
K = ln V – V i F
where Vi is the potential difference across the input, VF is the potential difference required to make the lamp flash and VL is a constant.
Design a laboratory experiment to test the relationship between T and R.
Explain how your results could be used to determine a value for K and VL.
You should draw a diagram, on page 3, showing the arrangement of your equipment. In your account you should pay particular attention to:
• the procedure to be followed
• the measurements to be taken
• the control of variables
• the analysis of the data
• any safety precautions to be taken.
Diagram
…… [15]
Mark scheme
1 Defining the problem
R is the independent variable and T is the dependent variable, or vary R and measure T 1
keep C constant 1
Methods of data collection
labelled diagram or correct symbols of workable circuit including: 1
• (d.c.) power supply correctly positioned
• (neon) lamp correctly positioned
do not accept ohmmeter in circuit
circuit diagram to determine resistance of resistors e.g. using ammeter and voltmeter OR ohmmeter 1
method to determine period or T, e.g. use a stopwatch / timer / oscilloscope 1
do not accept counting the flashes in a specified time
circuit diagram showing voltmeter(s) or oscilloscope(s) to determine Vi and VF 1
Method of Analysis
plots a graph of T against R 1
gradient 1
K=
C
gradient 1
VL = Vi − (Vi − VF ) eK = Vi − (Vi − VF ) e C
1 Additional detail including safety considerations Max 6
switch off (high voltage) circuit (before changing the resistor) / wear insulating gloves to prevent electrocution / shock D1
resistance of resistors linked to diagram is V / I for ammeter / voltmeter method or gradient of appropriate graph or resistance D2
from ohmmeter
input voltage or Vi is constant D3
repeat experiment for each value of R and average T D4
90 V (or larger) power supply D5
do not accept a.c. or signal generator
for stopwatch method: D6
time 10 or more flashes and divide by number of flashes
for oscilloscope method:
length of wave × timebase
record value of capacitance from the capacitor or method to determine capacitance D7
appropriate circuit to enable capacitance to be determined D8
relationship valid if a straight line passing through the origin is produced D9
method to obtain a measurable time period e.g. do a preliminary experiment to choose appropriate resistors, use large values D10
of R or C
A student is investigating the motion of a small steel ball in cooking oil. A measure of the oil’s resistance to the ball’s motion is called viscosity. Viscosity has the units pascal second (Pa s).
The student drops a ball into a cylinder of oil as shown in Fig. 2.1.
ball
cooking oil
heat
Fig. 2.1
The velocity of the ball is measured when it becomes constant and then the viscosity of the oil is determined.
The experiment is repeated for different temperatures of oil.
It is suggested that the viscosity η and the Celsius temperature θ are related by the equation
η = pθ q
where p and q are constants.
(a) A graph is plotted of lg η on the y-axis against lg θ on the x-axis.
Determine expressions for the gradient and the y-intercept.
gradient = ……
y-intercept = ……
[1]
(b) Values of θ and η are given in Fig. 2.2.
θ / °C η / 10–3 Pa s lg (θ / °C) lg (η / 10–3 Pa s)
38 41 ± 1
46 32 ± 1
55 25 ± 1
64 20 ± 1
72 17 ± 1
79 14 ± 1
Fig. 2.2
Calculate and record values of lg (θ / °C) and lg (η / 10–3 Pa s) in Fig. 2.2.
Include the absolute uncertainties in lg (η / 10–3 Pa s). [2]
(c) (i) Plot a graph of lg (η / 10–3 Pa s) against lg (θ / °C).
Include error bars for lg (η / 10–3 Pa s). [2]
(ii) Draw the straight line of best fit and a worst acceptable straight line on your graph. Both lines should be clearly labelled. [2]
(iii) Determine the gradient of the line of best fit. Include the absolute uncertainty in your answer.
gradient = …… [2]
1.65
1.60
lg (η / 10–3 Pa s)
1.55
1.50
1.45
1.40
1.35
1.30
1.25
1.20
1.15
1.10
1.55 1.60 1.65 1.70 1.75 1.80 1.85 1.90
lg (θ / °C)
(iv) Determine the y-intercept of the line of best fit. Include the absolute uncertainty in your answer.
y-intercept = …… [2]
(d) Using your answers to (a), (c)(iii) and (c)(iv), determine the values of p and q. Include the absolute uncertainties in your answer.
p = ……
q = ……
[3]
(e) Using your answers to (d), determine the temperature θ at which the viscosity of the cooking oil is 0.10 Pa s.
θ = …… °C [1]
[Total: 15]
Mark scheme
2(a) gradient = q 1
y-intercept = lg p
2(b) 1
1.58 or 1.580 1.61 or 1.613
1.66 or 1.663 1.51 or 1.505
1.74 or 1.740 1.40 or 1.398
1.81 or 1.806 1.30 or 1.301
1.86 or 1.857 1.23 or 1.230
1.90 or 1.898 1.15 or 1.146
absolute uncertainties in lg η: ± 0.01 to ± 0.03 1
2(c)(i) six points plotted correctly 1
must be accurate to the nearest half small square
diameter of points must be less than half a small square
error bars in lg η plotted correctly 1
all error bars to be plotted
total length of bar must be accurate to less than half a small square and symmetrical
2(c)(ii) line of best fit drawn 1
points must be balanced
do not allow line from top plot to bottom plot
if points are plotted correctly then lower end of line should pass between (1.820, 1.275) and (1.835, 1.275) and upper end of
line should pass between (1.640, 1.525) and (1.650, 1.525)
worst acceptable line drawn 1
steepest or shallowest possible line
mark scored only if all error bars are plotted
2(c)(iii) gradient determined with clear substitution of data points into ∆y / ∆x; distance between data points must be at least half the 1
length of the drawn line
must be negative
uncertainty = (gradient of line of best fit – gradient of worst acceptable line) 1
or
uncertainty = ½ (steepest worst line gradient – shallowest worst line gradient)
2(c)(iv) y-intercept determined by substitution of correct point into y = mx + c 1
y-intercept of worst acceptable line determined by substitution into y = mx + c 1
uncertainty = y-intercept of line of best fit – y-intercept of worst acceptable line, or
uncertainty = ½ (steepest worst line y-intercept – shallowest worst line y-intercept)
no ECF from false origin method
2(d) p = 10y -intercept 1
and
given to 2 or 3 sf
q = gradient 1
and
q and p have correct power of ten from (c)(iii) and (c)(iv)
absolute uncertainty in p = 10y −intercept of WAL − p 1
absolute uncertainty in q = uncertainty in gradient
correct substitution of numbers must be seen
2(e) 100 1
θ =q or
p
lg (100 ) − lg p
2 − y − intercept
lg θ = =
q gradient
correct substitution of numbers must be seen
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On this page, free: the mark scheme for AS & A Level Physics 9702/52, February/March 2019 (9702_m19_ms_52), and the question paper (9702_m19_qp_52), to read or download, with each question's marking points written out underneath.
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Physics 9702/52 for February/March 2019 is out of 30 marks, with 1 hour 15 minutes to answer it.
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