Transferring Electrical Energy Worksheet Page 44
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46M19.
(a)
1.8 (p)
these 4 marks can be broken down as follows:
1 mark for correct transformation and substitution into efficiency
equation
ie 0.8 × 1200 – useful power
PLUS
1 mark for useful power = 960 W / 0.96 kW
PLUS
1 mark for waste energy transferred = 0.24 × 0.5
or
waste energy transferred = 0.12 (kWh)
PLUS
1 mark for cost = 0.12 × 15
where a mathematical error has been made full credit should be
given for subsequent correct method
4
(b)
the waste energy is transferred as heat and sound
1
to the surroundings where it spreads out / is shared by
surrounding particles
accept air for surroundings
1
[6]
M20.
(a)
48
allow 1 mark for calculating energy as 3.2 kWh
2
(b)
largest power and longest time to run
1
[3]
Page 44 of 46
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