Download P2 Topic 2 - Using electricity foundation

Name: _______________________________________________
P2 Topic 2 - Using electricity
foundation
Date:
Time: 28 minutes
Total marks available: 28
Total marks achieved: ______
Questions
Q1.
Using electrical heating
Victor rides a motorbike.
He buys a kit to heat its handlebars in winter.
The kit has two handle bar grips.
Each grip contains an electrical heating coil.
(a) Complete the sentence by putting a cross ( ) in the box next to your answer.
When the coils are switched on, they get hot because
(1)
A current is lost in the coils
B energy is transferred in the coils
C resistance is transferred in the coils
D atoms flow through the coils
(b) The kit also has a three position switch and a 2.4 ohm resistor.
The diagram shows how Victor connects the parts.
Victor wants to check the voltage of the battery.
Add a meter to the diagram to show how to measure the battery voltage.
(2)
(c) Victor moves the switch to the ‘high heat’ position.
The 12 V battery produces a current of 2.5 A in the circuit.
(i) Calculate the electrical power produced.
(2)
electrical power = ...................................... W
(ii) R = V / I
Calculate the total resistance of the circuit.
(2)
total resistance = ...................................... Ω
(d) Victor moves the switch to the ‘low heat’ position.
The grips do not get as hot.
Explain why the grips are not as hot.
(2)
..............................................................................................................................................
..............................................................................................................................................
..............................................................................................................................................
..............................................................................................................................................
(e) The 2.4 ohm resistor must be fixed somewhere on the motorbike frame where it cannot be touched
by the rider.
Suggest a reason why.
(1)
..............................................................................................................................................
..............................................................................................................................................
Q2.
A student sets up an experiment to measure the potential difference (voltage) across a filament lamp.
She changes the current through the lamp.
The diagram shows the circuit she used.
(c) Complete the sentence by putting a cross (
(i) The component X in the circuit diagram is a
) in the box next to your answer.
(1)
A diode
B fixed resistor
C thermistor
D variable resistor
(ii) The meter that measures potential difference is
(1)
A in parallel with the power supply
B in parallel with the lamp
C in series with the lamp
D in series with the component X
(iii) Describe how the student should increase the current in the lamp.
(2)
..............................................................................................................................................
..............................................................................................................................................
..............................................................................................................................................
..............................................................................................................................................
(b) The student recorded these readings.
current / A
0.00
0.20
0.31
0.37
0.42
0.44
Four points are plotted on the graph.
potential difference / V
0.0
2.0
4.0
6.0
8.0
10.0
(i) Plot the points for 2.0 V and 8.0 V.
(1)
(ii) Draw the line of best fit.
(1)
(c) Calculate the resistance of the lamp when the current is 0.44 A and the potential difference is 10.0
V.
(2)
resistance = . . . . . . . . . . . . . . . . . . . . . . Ω
(d) Describe the energy transfer that takes place in the lamp.
(2)
..............................................................................................................................................
..............................................................................................................................................
..............................................................................................................................................
..............................................................................................................................................
(Total for Question is 10 marks)
Q3.
The students want to measure both the current in the lamp and the potential difference (voltage)
across the lamp.
(i) Complete the circuit below with an ammeter and a voltmeter correctly connected.
The power supply, variable resistor and lamp symbols are already drawn for you.
(3)
(ii) The current in a lamp is 0.5 A.
Its resistance is 8 Ω.
Calculate the potential difference (voltage) across the lamp.
(2)
..............................................................................................................................................
Q4.
An inventor is designing a battery-powered torch.
She wants the torch to have a brightness control.
She builds this circuit to test the lamp in the torch.
(i) Add a voltmeter to the circuit which will measure the potential difference (voltage) across the lamp.
(1)
She sets the control at the "bright" position.
The current is 0.26 A and the potential difference (voltage) across the lamp is 6.0 V.
Calculate the resistance of the lamp.
(2)
..............................................................................................................................................
Q1.
No Examiner's Report available for this question
Q2.
(a)(iii)
This question showed that candidates do have an understanding of how the current in a circuit can be
controlled. Increasing the voltage or decreasing the resistance were both equally popular answers.
Results Plus: Examiner Comments
This answer was awarded 2 marks for 'higher voltage'.
Either 'change the battery' or 'change the variable resistor to a fixed resistor' would qualify for 1
mark.
Results Plus: Examiner Tip
When stating as an answer that a quantity will change, remember to explain what the
change will be, ie bigger or smaller, increase or decrease.
(b)
Most candidates could score at least 1 mark in their answers to this question. Marks were lost by
candidates not reading the question carefully and so not realising that not only have points to be
plotted but the line of best fit also has to be drawn.
Results Plus: Examiner Comments
The point (8.0,0.42) has been plotted incorrectly and the point at the origin has been
ignored in attempting to draw the line of best fit. No marks were awarded.
Results Plus: Examiner Tip
Check the graph scale before plotting points. Consider all the points when drawing a
line of best fit.
Results Plus: Examiner Comments
An incorrect point has been plotted but there is a reasonable line of best fit although it
does not go through the top point. 1 mark was awarded.
Results Plus: Examiner Tip
Remember that the line of best fit may be a curve.
Results Plus: Examiner Comments
This response scored 2 marks.
The points are plotted correctly. The line goes through the origin and has a reasonable
distribution of points on either side.
(c)
This question was generally answered well but some candidates were unable to correctly insert
values into an equation that they were given and others are unable to complete the division
correctly.
Results Plus: Examiner Comments
This response includes the substitution and correctly takes the answer to two significant
figures (although significant figures were ignored for this calculation). 2 marks were
awarded.
Results Plus: Examiner Comments
This response scored 1 mark for showing the substitution, although the final answer is
incorrect.
Results Plus: Examiner Tip
Always show the examiner what you are doing with numerical values, do not just give
the answer.
Results Plus: Examiner Comments
This candidate could correctly substitute but either did not understand the meaning of
the division sign or was using the calculator incorrectly. 1 mark was awarded.
Results Plus: Examiner Tip
Make sure you can divide correctly.
Results Plus: Examiner Comments
Candidates must know what the symbols used in the equation mean. This answer did
not receive any marks.
Results Plus: Examiner Tip
Use the formulae sheet at the front of the examination paper. This gives the equations
in both words and symbols.
(d)
A large number of candidates did not mention any type of energy in their answer. The simple
answer of 'electrical energy is converted to light and heat' was not often given.
Results Plus: Examiner Comments
This answer mentions light but not as a form of energy and so was not awarded any
marks.
Results Plus: Examiner Comments
This answer does not give the name of the energy that was lost and therefore does not
score any marks.
Results Plus: Examiner Tip
Remember to name energy types when dealing with energy transfer.
Q3.
(i)
Most candidates could draw the correct symbols for at least one ammeter or voltmeter and they
usually put ammeter in series. Candidates were less confident in recalling that the voltmeter
should be connected in parallel with the bulb. The most common error was placing the voltmeter
in series with the bulb and the ammeter followed by having the voltmeter in parallel with the
variable resistor, the battery or even random sections of the connecting wires. Most candidates
used a pen to draw the wiring diagram and then added the meters so that they had an (incorrect)
line drawn through the symbol which was not penalised.
Only 15% of candidates failed to score any marks on this question and 23% scored all 3 marks.
This response was the most common way that one mark was scored.
Results Plus: Examiner Comments
One mark for a correct meter symbol.
This response scored 3 marks
Results Plus: Examiner Comments
The error in connecting to the variable resistor was ignored.
(ii)
Most candidates did the correct substitution and evaluation. As before a significant number
divided instead of multiplying and too many failed to show any working.
One of the many responses scoring both marks.
Results Plus: Examiner Comments
Correct substitution and evaluation.
One of the candidates who chose to divide 8 by 0.5.
Results Plus: Examiner Comments
Would the same mistake have been made if the equation was copied out?
Q4.
i
The majority of candidates knew the correct symbol for a voltmeter but most of them placed the
voltmeter in series with the other components. A large number seemed to know that it had to be
placed in parallel with something but then placed it across the ammeter or the battery.
The voltmeter must be connected across the lamp to measure the voltage across the lamp.
Results Plus: Examiner Comments
This is a correct answer.
Results Plus: Examiner Comments
This is an incorrect answer.
ii
Because the formula at the front of the booklet has V as the subject of the equation, candidates
were provided with a box containing the re-arranged expression for calculating current. Most
candidates were able to substitute the correct values into this expression. The evaluated answer
was not a whole number and better candidates were able to round this to a suitable number of
significant figures to give an answer of 23. Examiners would, however, accept a value which
could be rounded down to 23.
Mark Scheme
Q1.
Question
Number
(a)
Acceptable answers
Answer
Acceptable answers
• voltmeter symbol
(1) • connected
across battery (1)
(b)
Question
Number
(c)(i)
Answer
substitution (1) 2.5 ×
12 evaluation (1) 30
(W)
Question
Number
(c)(ii)
Answer
substitution (1) 12 ÷
2.5 evaluation (1) 4.8
(Ω)
Question
Number
Mark
(1)
B
Question
Number
(d)
Answer
Answer
An explanation
linking any two of
Mark
(2)
Acceptable answers
give full marks for
correct answer, no
working
Mark
(2)
Acceptable answers
give full marks for
correct answer, no
working
Mark
(2)
Acceptable answers
Mark
(2)
the following points
• greater resistance
in the circuit (1)
• less current (in the
circuit) (1) • less
energy transfer in the
coils (1) • less
voltage across the
coils (1) • less
power generated in
the coils (1)
Question
Number
(e)
Answer
Acceptable answers
Any one from the
following points
• heat will be
generated in the
resistor • it will get
hot • could burn the
rider
Mark
(1)
Q2.
Answer
(a)(i)
(a)(ii)
(a)(iii)
D variable resistor
B in parallel with the
lamp
A description
including
 resistance
changed (1)

reduced/decreased/l
owered (1)
OR
(b)(i)
(b)(ii )
 voltage/p.d
/EMF (of supply)
changed (1)
 increased
/turned
up/higher(1)
both points correct
(1)
curve of best fit
judged by eye (1)
Acceptable
answers
Mark
(1)
(1)
(2)
remove (variable)
resistor /component
X (2)
number of
batteries/number of
cells
add another
cell/battery/battery
pack/power
pack/power supply
(2)
allow + / - half
square
Must pass through
zero and two other
points.
5th point can be
either (8.0,0.42)
or
(8.0,
0.44)
straight
line of best fit
(1)
(1)
through origin
tolerance between
lines A and B shown
on the diagram
(c)
(d)(i)
substitution (1)
10/0.44 or 250/11
evaluation (1)
23 (ohms)
an explanation
linking two of the
following points
 electric(al
)(energy) (1)
 (is converted) to
heat / thermal
(energy) (1)
 (is converted) to
light (1)
5th point can be
either (8.0,0.42)
or
(8.0, 0.44)
give full marks for
correct
answer, no working
22.7(ohms),22.73
(ohms),
22.72(ohms)
Ignore excessive
decimal places.
electricity
(2)
(2)
Total marks for question =10
Q3.
Answer
(i)
correct symbol for
ammeter or
voltmeter (seen
anywhere) (1) one
meter connected in
parallel with
lamp/variable
resistor/supply and
one meter in series
with lamp(1)
both
meters correctly
connected (ammeter
in series and
voltmeter in parallel
with lamp)
(1)
Acceptable
answers
Ignore gaps, lines
through symbols and
wire connected to
side of variable
resistor Symbols do
not have to be
correct for this mark
voltmeter connected
across both
components is same
as voltmeter
connected across
supply Symbols do
not have to be
correct for this mark
any shape, labelled
ammeter, in series
Mark
(3)
(ii)
substitution
0.5 × 8
evaluation
4 (V)
with lamp AND any
shape, labelled
voltmeter, in parallel
with lamp gains
marking points 2 and
3
bald 4.0 x 10n
gains 1 mark eg bald
40 or 0.4 = 1 mark
(BOD for correct
substitution) give
full marks for correct
numerical answer, 4
(V) even if no
working
(1)
(1)
(2)
Q4.
Answer
(i)
connected in
parallel with lamp (1)
(ii)
Substitution
R = 6.0 /
0.26
(1)
Evaluation
=
23
)
Acceptable
answers
recognisable symbol
such as a box with
letter V inside or box
with the word
voltmeter inside it
accept voltmeter
across both lamp
and ammeter
Mark
(1)
An answer which
rounds to 23 Give full
marks for correct
answer no working
(1
(2)