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EE5: Practical Electricity – Power Voltage Current Resistance 1. A student sets up the following circuit to investigate the resistance of a resistor. The variable resistor is adjusted and the voltmeter and ammeter readings are noted. The following graph is obtained from the experimental results. (a) (i) Calculate the value of the resistor R when the reading on the voltmeter is 4.2V (3) (ii) Using the information from the graph, state whether the resistance of the resistor R1, increases, stays the same or decreases as the voltage increases. Justify your answer. (2) (b) The student is given a task to combine two resistors from a pack containing one each of 33Ω, 56Ω, 82Ω, 150Ω, 270Ω, 390Ω. Show by calculation which two resistors should be used to give: (i) The largest combined resistance (3) (ii) The smallest combined resistance. (3) 2 Party lights consist of 16 identical lamps connected in series. They operate from a 24 volt power supply. The current in the circuit is 1.25 amperes. (a) (b) (c) (d) 3. Calculate the total resistance of the lamps in the circuit. Calculate the voltage across each lamp. Calculate the power of each lamp One lamp stops working. What happens to the rest? Parking sensors are fitted to the rear bumper of some cars. A buzzer emits audible beeps, which become more frequent as the car moves closer to an object. The sensor operates at a voltage of 12 V and has a current range of 20–200 mA. Calculate the maximum power rating of the sensor. 4. (3) (3) (3) (1) (3) An MP3 player is put on a docking station with external speakers. Calculate the voltage across a 10 W speaker if its resistance is 8 ohms. (3) 5. Scottish power measures the electrical energy you use in your house in a unit called kilowatt hours (kWh) ( 1kWh = 1000 x 60 60 = 3,600,000 J ) Scottish Power charges 12p for 1 kWh of energy. How much does it cost if you leave an 11W energy saving lightbulb on all night for 10 hours. (3) Total (30)