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Questions Q1. Complete the sentence by putting a cross ( An electric current is the rate of flow of ) in the box next to your answer. (1) A B C D atoms charge voltage watts Q2. The diagram shows a simple generator connected to a lamp. The magnet is made to spin at a steady speed. The ammeter gives a reading of 1.5 A. The voltmeter gives a reading of 6 V. (i) Calculate the output power of the generator. (2) .............................................................................................................................................. (ii) State two changes to the design of the generator that would give a larger output power for the same speed of rotation. (2) .............................................................................................................................................. .............................................................................................................................................. (iii) This generator supplies an alternating current (AC) to the lamp. Other types of generators supply a direct current (DC). Describe the difference between charge movement in a direct current and in an alternating current. (2) .............................................................................................................................................. .............................................................................................................................................. Q3. Alternating current and its uses The diagram shows a generator producing an alternating voltage. (a) Draw one straight line from each letter to its correct label. (2) (b) The generator is connected to a lamp. The current in the lamp is alternating. (i) Which of these is an alternating current? Put a cross ( ) in the box next to your answer. (1) (ii) The generator is turned faster. Explain what happens to the lamp. (2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. (c) A larger generator produces a current of 2 A at a voltage of 12 V. Calculate the electrical power generated. State the unit. (3) power generated =........................... unit =........................... (d) Transformers are designed to use alternating current. Describe what change happens when a step-up transformer is used. (2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. Q4. The photograph shows Alan’s bike-powered generator. Alan pedals at a steady speed. (i) The output voltage of the generator is 12.3 V. The output current is 8.00 A. Calculate the output power of the generator. (2) output power = ............................................... W (ii) Alan supplies 15 600 J to the generator in 120 s. Calculate the input power to the generator. (2) input power = .............................................. W Q5. A television has a power of 400 W. The cost of 1 kW h of electrical energy is 15p. Calculate the cost of using the television for 10 hours. (3) .............................................................................................................................................. Q6. A solar panel generates direct current. (i) Describe the difference between direct current and alternating current. (2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. (ii) The output from the solar panel is 60 V. State why a transformer cannot be used to increase this voltage. (1) .............................................................................................................................................. .............................................................................................................................................. Q7. A LED lamp has a power rating of 3 W. The voltage across the lamp is 12 V. Calculate the current in the lamp. (3) current in the lamp =. . . . . . . . . . . . . . . . . . . . .A Q8. Scientists say that graph 1 shows an alternating current while graph 2 shows a direct current. The two graphs differ in several ways. State the difference between the currents which makes one alternating and the other direct. (1) .............................................................................................................................................. .............................................................................................................................................. Q9. A homeowner fits a solar panel to her roof. The cost of the solar panel is £4800. The solar panel supplies an average of 800 kW h of electrical energy to the National Grid each year. The homeowner is paid 40p for each kW h of energy supplied to the National Grid. Calculate the payback time for the solar panels by selling energy to the National Grid. (3) payback time = ......................................................... years Mark Scheme Q1. Answer B Acceptable answers Mark (1) charge Q2. Answer (i) Substitution (1) 1.5 × 6 Evaluation (1) 9 (W) Ignore any unit given by candidate. (ii) More turns on the coil (1) More powerful/stronger magnet(s) (1) (iii) A description including in one direction only for DC (1) reversing direction for AC (1) Acceptable answers Power of 10 error max 1 mark Give full marks for correct answer with no working shown Mark (2) Wrap coils on iron (core/former)/ more coils/twists/loops. Bigger coil is insufficient. More magnets. Bigger/larger magnet is insufficient. (2) Ignore increase speed of rotation (2) 'DC goes straight' is insufficient AC switches/changes direction OR moves to and fro 'AC goes different ways' is insufficient. Diagram with labelled arrows could get 2 marks. Q3. Question Number (a) Answer Question Number (b)(i) Question Number (b)(ii) Answer Acceptable answers (2) Mark B Answer Acceptable answers (1) Mark Question Number (c) Question Number (d) Acceptable answers Mark More than one line bfrom either P or Q (or both) loses the mark for that box An explanation linking the following • increased brightness (1) • (due to) increased voltage (1) Answer ‘fuses’ / ‘blows’ / gets hotter Acceptable answers (1) Mark substitution (1) 2 x 12 Give full marks (2) for evaluation (1) 24 unit correct answer, no (1)W working (accept bald 2.4 for substitution) = 1 watt(s), AV, VA, J/s If only one number and one unit their position is immaterial otherwise, mark the number in the power generated space and the unit in the unit (3) space Answer Acceptable answers Mark A description including the following • voltage (1) • increases (1) current decreases (ignore speed of current) Accept for 1 mark • increases current AND reduces voltage • voltage higher and bigger current/power • power decreases ‘it’ increases/decreases =0 (3) Q4. Question Number (i) Question Number (ii) Answer Acceptable answers substitution (1) (output power =) 8.00 × 12.3 evaluation (1) 98.4 (W) Answer give full marks for correct answer, no working substitution (1) (input power =) 15600 ÷ 120 evaluation (1) 130 (W) give full marks for correct answer, no working Answer Conversion 0.4 (kW) (1) Substitution 0.4 × 10 ×15 (p) (1) or 0.4 × 10 × 0.15 (£) Evaluation 60(p) or £0.6 (1) Acceptable Mark answers (3) give marks for correct answer, no working 60(p) or £0.6 (3) 60,000(p) or £600 (2) 6 to any other power of 10 (1) (400/40/4) × 10 × (15/0.15) gains one mark if no mark can be awarded for evaluation. Answer Acceptable answers a description including the following • direct current (the flow of charge) is only in one direction (1) • alternating current (the flow of charge periodically) changes / reverses direction / eq (1) Answer d.c stays positive/negative only goes positive and negative any one of the following It is not alternating (1) / direct current Acceptable answers Mark (2) Mark (2) Q5. Q6. Question Number (i) Question Number (ii) Acceptable answers Mark (2) Mark • transformers only change alternating voltages / currents • transformers will not work with direct current Q7. Answer Acceptable Mark answers substitute (1) Subst. and transform. 3 = I × 12 either order transformation (1) 1 mark only can be I = 3 ÷ 12 evaluation scored for correct (1) substitution after 0 .25 (A) Ignore any incorrect unit given by transposition. Accept candidate any number of sig. figs. that rounds to 0.25 (A) 250 mA gains 3 marks give full marks for correct answer, no working 2.5 × any other power of ten = 2 marks eg 25 (A) (3) gains 2 marks Q8. Question Number Answer Acceptable answers Mark alternating current can take positive and negative values RA (1) a.c. above and below zero /the line a.c. goes one way and then the other RA (1) Answer Acceptable answers Mark substitution (1) 800 × 0.4 / 800 × 40 evaluation of payment (1) (£)320 / 32000 (p) evaluation of payback time (1) 15 (years) 4800 / 0.4 = 12000 Kwh (to be sold) takes 12000 / 800 years substitution and transposition can be in either order allow power of 10 error in 15 for (2) give full marks for correct (3) answer, no working Q9. Question Number