P2 Revision Booklet

Energy in Circuits

Medium (Grade C)

Q1.          The picture shows an advert for an electric mobility scooter.

(a)     The batteries are joined in series.

(i)      What is the potential difference provided by the batteries to the motor?
...........................................................................................................................
(1)

(ii)     The batteries supply a direct current (d.c.).
         What is a direct current (d.c.)?
...........................................................................................................................
...........................................................................................................................
(1)

(b)     At 2.5 m/s on flat ground, the motor takes a current of 3.0 A from the batteries.
(i)      Explain why a bigger current is taken from the batteries when the scooter is going uphill at 2.5 m/s.
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(2)
(ii)     What effect does travelling uphill have on the range of the scooter?
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(1)

(c)     The mass of the scooter driver is 80 kg.
          Use the equation in the box to calculate the kinetic energy of the scooter and driver when they are travelling at maximum speed.

 

Q2.          The diagrams show a hair-dryer and the circuit inside the hair-dryer.

(a)     Switches S1, S2 and S3 are all shown in the OFF position.
          Which switch or switches have to be ON to make:
(i)      only the fan work? ............................................................................................
(ii)     both heaters work? ............................................................................................
(2)

(b)     (i)      What happens to the current in the circuit when the heaters are switched on?
...........................................................................................................................

(ii)     Suggest why it is important to have the fan working when the heaters are switched on.
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(3)

(c)     This hair-dryer has a plastic case. It is connected to a mains socket by a 3-pin plug.
The cable connecting the hair-dryer to the plug contains only two wires.
(i)      Write down the colour of the insulation on the wires.
Wire 1 ...............................................................................................................
Wire 2 ...............................................................................................................

(ii)     Which of the usual three wires is not needed?
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(iii)     This hair-dryer is safe to use without the third wire. Explain why.
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(5)

(d)     The following information is stamped on the hair-dryer.

(i)      Which number tells us how fast the hair-dryer uses energy?
...........................................................................................................................
(ii)     On what else does the energy used by the hair-dryer depend?
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(2)
(Total 12 marks)

 

Q3.          A student investigates how the current flowing through a filament lamp changes with the voltage across it.
She is given a filament lamp and connecting wires.
She decides to use a 15V power supply, a variable resistor, an ammeter, a voltmeter and a switch.

(a)     Complete the circuit diagram to show how she should set up the circuit.

 

 
(4)

(b)     The student obtains the following results.
VOLTAGE (V)	0.0 	3.0 	5.0 	7.0 	9.0 	11.0	
CURRENT (A)	0.0 	1.0 	1.4 	1.7 	1.9 	2.1	

(i)      Plot a graph of current against voltage.

(3)

(ii)     Use your graph to find the current when the voltage is 10V.
Current .................... A
(1)

(iii)     Use your answer to (ii) to calculate the resistance of the lamp when the voltage is 10V.
...........................................................................................................................
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Resistance .................... Ω
(2)

(c)     (i)      What happens to the resistance of the lamp as the current through it increases?
...........................................................................................................................

(ii)     Explain your answer.
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(2)
(Total 12 marks)

 

Q4.          (i)      Write the equation which shows the relationship between the electric current,
the power and the voltage.
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.....................................................................................................................................
(1)

(ii)      Calculate the power if the current is 5 A and the voltage is 400 000 V. Show clearly how you work out your answer and give the unit.
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.....................................................................................................................................
Power = .............................................
(2)
(Total 3 marks)

 

Energy in circuits-Mark scheme
 
M1.          (a)     (i)      24(V)
1
(ii)     current always flows in the same direction
         or current only flows one way
1

(b)     (i)      more power / force needed
accept energy transformed faster
1
         work done to lift the scooter uphill
accept it moves against gravity
         or work done against gravity
accept energy is transformed to gravitational potential energy
1

(ii)     reduces it
1

(c)     375
1 mark for correct substitution
1 mark for an answer = 250
1 mark for an answer = 125
2
[7]

 

M2.          (a)     (i)      S3
for 1 mark
1
(ii)     S1, S2 and S3
for 1 mark
1

(b)     (i)      increases/current passes through heaters/current unaffected in fan
for 1 mark
1
(ii)     (fan) blows/air moving prevents dryer overheating
for 1 mark each
2

(c)     (i)      brown
blue
any order
for 1 mark each
2

(ii)     earth/green and yellow
for 1 mark
1

(iii)     (case is) plastic
plastic does not conduct (electricity)
for 1 mark each
2

(d)     (i)      1300/power
for 1 mark
1
(ii)     time/units of time
for 1 mark
1
[12]

 

M3.          (a)     4 symbols correct accept
(accept  for bulb; lose 1 mark if line through symbols, lose 1 mark if circuit incorrect, switch may be open or closed)
(allow  or )
gains 1 mark
4

          but
all correct
gains 2 marks
          ammeter in series with lamp
for one mark
          voltmeter in parallel with lamp / lamp and switch / lamp, switch and ammeter
for one mark

(b)     (i)      5 points correctly plotted
allow (0, 0) correct if graph goes through the origin even if no × or O
gains 1 mark
         but
6 points correctly plotted
gains 2 marks
         smooth curve through points – not straight line / curve + straight line
for one mark
3

(ii)     2 (A)
         allow  0.05 (½ square) from candidates’ graph
for one mark
1

(iii)     R = V / I   or   R = 10 / 2
gains 1 mark
         but
R = 5 (Ohms)      ecf
gains 2 marks
2

(c)     (i)      resistance increases
for one mark
(ii)     temperature (of filament) has increased / filament gets hot
for one mark
2
[12]

 

M4.          (i)      power = current × voltage
or any correctly transposed version
accept watts = amps × volts
accept P = IV
do not credit P = CV
accept p.d. for voltage triangle acceptable only if used correctly in (ii)
1

(ii)      2 000 000 (1)
2000 kilowatts/kW (2)
accept KW
          watts/W (1)
2 megawatts/MW (2)
do not credit mW (1) if correct method is clearly shown but answer is numerically incorrect or unit is absent or incorrect
do not credit any working from an incorrect equation in (d)(i) but an appropriate unit should be credited
2
[3]