For teacher [ Answer Key ]

1. © Oxford University Press 2016 www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original. 1
P5 Summary answers
Student Book answers
Question
number
Answer Marks Guidance
1 a i neutral 1
1 a ii live 1
1 b i waves taller
as amplitude increases
1
1
1 b ii waves closer together
as time for each cycle is less
1
1
2 a if live wire touches case, case becomes live
anyone touching case electrocuted as electric current passes through their
body to earth
1
1
2 b live: brown, neutral: blue, earth: green and yellow 1
3 a so any appliance connected to wall socket can be switched on or off
without affecting any appliance connected to a different wall socket
1
1
GCSE Physics only
3 b if too much current fuse melts
and cuts current off
1
1
4 a i 2500 W/230 V
= 11 A
1
1
4 a ii 13 A fuse 1
4 a iii 2500 W × (6 × 5 × 28) s
= 2.1 MJ
1
1
4 b kettle,
power > twice power of oven
and used less than oven each day
1
1
1

2. © Oxford University Press 2016 www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original. 2
P5 Summary answers
Student Book answers
Question
number
Answer Marks Guidance
4 c energy → kettle in 300 s = 2500 W × 300 s = 750 000 J
energy → water = 1.5 kg × 4200 J/kg °C × (100 – 15) °C = 540 000 J
1% efficiency =
540 000 J
750 000 J
x 100%
= 71%
1
1
1
1
5 a circuit diagram with 5 Ω resistor in series with bulb, switch and 12 V battery 1
5 b i 0.6 A × 60 s × 12 V
= 432 J
1
1
5 b ii W = (0.6 A)2 × 5 Ω = 1.8 W
E = 1.8 W × 60 s = 108 J
1
1
5 b iii 432 J − 108 J
= 324 J
1
1
5 c i 5 Ω + 25 Ω = 30 Ω 1
5 c ii 12 V/30 Ω
= 0.40 A
1
1
5 c iii battery power = 0.40 A  12 V = 4.8 W
power to 5 Ω resistor = I2
R = 0.402
 5 = 0.80 W
power to 25 Ω resistor = I2
R = 0.402
 25 = 4.0 W
1
1
1
6 a i = 36 W/12 V
= 3.0 A
1
1
6 a ii 3.0 A × 200 s
= 600 C
1
1
6 b i 36 W × 200 s
= 7200 J
1
1
6 b ii 12 V or 7200 J/600 C
= 12 J/C
1
1

3. © Oxford University Press 2016 www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original. 3
P5 Summary answers
Student Book answers
Question
number
Answer Marks Guidance
6 c i 3.0 A through each bulb
6.0 A ( = 2 × 3.0 A) through battery
1
1
6 c ii energy per second to each bulb = 36 W = 36 J/s
energy per second from battery = 12 V × 6.0 A = 72 J/s
 energy supplied per second to two bulbs = energy supplied per second
by the battery
1
1
1
7 a 6600W
230V
= 28.7 A
1
1
7 b i D or E
because maximum safe current through D and E > current when oven
operates at full power
so D and E would not overheat
1
1
1
7 b ii A, B and C overheat as maximum safe current < oven at full power,
over-heated cable → fire or cable insulation may melt and start fire due to
short-circuit
1
1

4. © Oxford University Press 2016 www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original. 4
P5 Summary answers
Student Book answers
Question
number
Answer Marks Guidance
GCSE Physics only
8 correct circuit diagram similar to P5.4 Figure 2,
any four from:
check both meters read zero when switch open, set variable resistor to
maximum resistance and close switch,
measure lamp current and p.d. from ammeter and voltmeter and record
measurements in table,
adjust variable resistor to increase current in steps, at each step repeat
and record measurements,
add third column to table for power supplied to lamp and use equation P =
I × V to calculate power at each step,
plot graph of power against current .
2
4
circuit correct except for one component
gains 1 mark.