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GCSE Physics for CCEA second edition31. a) energy = ?, power = 960 W, time = 60 senergy = power x time= 960 W x 60 s= 57 600 Jb) current = ?, voltage = 12 V, power = 960 WP = V x I960 W = 12 V x I960I = 80 A1232. current = 4 A, voltage = 240 V, power = ?P = V x I= 240 V x 4A= 960 W33. current = ?, voltage = 12 V, power = 48WP = V x I48 W = 12 V x I48I = 4 A1234.Name of applianceBulb of study lampTelevisionToasterConvector heaterShowerPower rating60 W80 W120 W2 kW3 kW35. resistance = 48, voltage = 240 V, power = ?22V 240P = 1200 WR 48PVCurrent I Resistance R VI60 240 0.25 A 960 2400.2580 240 0.33 A 720 2400.333120 240 0.5 A 480 2400.52000 240 8.33 A 28.8 2408.333000 240 12.5 A 192 24012.536. a) i) Brown.ii) Blue.iii) Green and yellow.b) i) Current will flow from the live wire, through the metal case to the person touching thecase, and then to earth. The person touching the case would be electrocuted.34
GCSE Physics for CCEA second editionii) Since the earth wire is now properly connected, the current will flow through the earthwire to the ground, melting the fuse, cutting off the current. The person touching the casewould not be electrocuted.37. a) Direct current – always flows in the same direction, from a fixed positive terminal to thefixed negative terminal of a supply. See Figure 39 b, page 133.b) Alternating current – the voltage (and hence the current) change size and direction in aregular and repetitive way. See Figure 40, page 133.38. Circuit breakers react much more quickly than fuses so protecting the user.39. a) current = ?, voltage = 230 V, power = 60WP = V x I60 W = 230 V x I60I = 0.26 A230b) A fuse rated greater than 3 A would pass too high a current which would be dangerous.40. a) current = ?, voltage = 240 V, power = 3000WP = V x I3000 W = 240 V x I3000I = 12.5 A i.e. the fuse would ‘blow’.240b) current = ?, voltage = 240 V, power = 60 WP = V x I60 W = 240 V x I60I = 0.25 A240If a 13 A fuse was used, the fuse would not ‘blow’ until the current exceeded 13 A. So afaulty study lamp would electrocute user.c) current = ?, voltage = 240 V, power = 800 WP = V x I800 W = 240 V x I800I = 3.33 A240So a 5A fuse would be preferable.41. Consider 1 bulb:current = ?, voltage = 240 V, power = 60 WP = V x I60 W = 240 V x I60I = 0.25 A240So you should use less than 20 bulbs so that the fuse would not be overloaded.35
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