Oxford Revise AQA GCSE Combined Science Foundation | Chapter P3 answers

P3: Supplying electricity

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Answers

Extra information

Mark

AO / Specification reference

01.1

230 V

1

AO1

6.2.3.1

01.2

alternating

1

AO1

6.2.3.1

01.3

step down

1

AO1

6.2.4.3

02.1

the live wire — is attached to an alternating p.d. from the supply

the neutral wire — completes the circuit

the earth wire — is the safety wire

all lines correct for two marks

one line correct for one mark

2

AO1

6.2.3.2

02.2

live and neutral

1

AO1

6.2.3.2

02.3

no

case

cannot

1

1

1

AO1

6.2.3.2

03.1

1000 W

more

1

1

AO3

6.2.4.2

03.2

energy transferred = 700W × 60s

= 42 000

J

1

1

1

AO1

AO2

6.2.4.2

03.3

the mains

thermal

1

1

AO2

6.2.4.2

04.1

power = potential difference × current

= 6 × 1.5

= 9 W

1

1

AO1

AO2

4.2.4.1

04.2

\(
{\rm{power}} = \frac{{{\rm{energy}}}}{{{\rm{time}}}}
\)

1

AO1

4.1.1.4

04.3

\(
9 = \frac{{{\rm{energy}}}}{{{\rm{30}}}}
\)

energy = 9 × 30

= 270 (J)

accept 270 with no working for three marks

1

1

1

AO2

4.2.4.2

04.4

both devices transfer the same amount of energy

1

AO2

4.2.4.2

05.1

potential difference = 230 V

1

AO1

6.2.4.2

05.2

energy transferred = charge flow × potential difference

1

AO1

6.2.4.2

05.3

energy transferred = 10 × 230

= 2300 (J)

1

1

AO2

6.2.4.2

05.4

\(
{\rm{power}} = \frac{{{\rm{energy\ transferred}}}}{{{\rm{time}}}}
\) \(
= \frac{{{\rm{2300}}}}{{{\rm{15}}}}
\)

= 153.3 W

= 150 W

answer given to two significant figures

1

1

1

AO2

6.2.4.2

05.5

(chemical from the mains to energy in a), kinetic (store)

and thermal (store)

1

1

AO2

6.2.4.2

06.1

power = potential difference × current

1

AO1

6.2.4.1

06.2

power = 230 × 3.5

\(
= 805 \approx 800{\rm{W}}
\)

1

1

AO2

6.2.4.1

06.3

power = current2 × resistance

1

AO1

6.2.4.1

06.4

805 = (3.5)2 × resistance

805 = 12.25 × resistance

\(
\rm{resistance} = \frac{805}{12.2}
\) \( = 65.71 \approx 66 \)

1

1

AO2

6.2.4.1

06.5

metal conducts electricity

if the live wire touches the case and you touch the case, a current can flow through you

1

1

AO3

6.2.3.2

07.1

kettle

allo1 2.2 kW

1

AO2

6.2.4.1

07.2

power = current × potential difference

1

AO1

6.2.4.1

07.3

microwave

1

AO3

6.2.4.1

07.4

1100 = current × 230

\(
\rm{current} = \frac{1100}{230}
\)

= 4.8 A

1

1

1

AO2

07.5

current in kettle is double/twice/two times the current in the vacuum cleaner

1

AO3

6.2.4.1

08.1

insulating

slowly

thicker

1

1

1

AO2

6.1.2.1

08.2

glass

1

AO3

6.1.2.1

09.1

the National Grid

1

AO1

4.2.4.3

09.2

both transformers change the potential difference

the transformer near the power station/transformer 1 is a step-up transformer/increases the potential difference

the transformer near the house/transformer 2 is a step-down transformer/decreases the potential difference

1

1

1

AO1

4.2.4.3

09.3

(the energy is transferred at a high potential difference so) the current is small

so the energy/power/heat lost is small

1

1

AO1

4.2.4.3

10.1

the potential difference of the mains electricity in the UK is – about 230 V

the frequency of mains electricity in the UK is – 50 Hz

the mains supply in the UK produces a current that is – alternating

1

1

1

AO1

4.2.3.1

10.2

Earth or neutral

Earth; neutral in any order

live; neutral in any order

either word for the mark

either order for the mark

either order for the mark

1

2

2

AO1

4.2.3.1

10.3

if the casting on an appliance becomes live, the earth wires conducts the current safely to earth

do not accept ‘to protect the user’

1

AO1

4.2.3.1

11.1

power of solar cells = 10 W

power of wind turbine = 0.4 W

number × 0.4 = 10

\(
{\rm{number}} = \frac{10}{0.4} = 25
\)

allow 25 without calculation for two marks

1

1

AO2

11.2

cost of 25 wind turbines = 200 × 25

= £5000

1

11.3

cost of solar cells = £12 000

the cost of the wind turbines is much less than that of the solar cells

the wind turbines take up space/affect the ecosystem

there are fewer environmental issues with solar cells

comparison

1

1

1

AO3

6.2.4.1

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