124 Chapter 6 • Electricity Exercise 6.7


1. A 220 volt electric heater is rated at 1,6 kW. Determine; 1.1 the current it would draw from the supply, and 1.2 the resistance of the heating element.


(7,27 A; 30,26 ohms)


2. A resistor has a value of 30 ohms and draws a current of 1,5 amperes when connected across a certain supply. Calculate; 2.1 the power consumption, and 2.2 the supply voltage.


3. When a 12 volt lamp is connected across the correct supply voltage, its power consumption is 60 watts. Determine; 3.1 the rated current, and 3.2 the resistance of the filament.


4. A lamp filament has a resistance of 121 ohms and draws a current of 0,91 amperes when connected across a certain supply. Determine; 4.1 the power consumed by the lamp, and 4.2 the supply voltage.


5. A 220 volt electric kettle is rated at 1,2 kW. Calculate; 5.1 the rated current, and 5.2 the resistance of the heating element.


Exercise 6.8


1. Will the total resistance of a circuit increase or decrease when a resistor is connected in series with it?


2. What is remarkable about the current in a series circuit? 3. Determine the total resistance of three resistors with values of 3 ohms, 6 ohms and 2,5 ohms respectively, when connected in series.


(11,5 ohms)


4. Tree resistors of 5 ohms, 6 ohms and 13 ohms are connected in series across a 12 volt supply. Calculate; 4.1 the total resistance of the circuit, and 4.2 the current drawn from the supply.


5. Tree resistors of 4 ohms, 12 ohms and 15 ohms respectively are connected in series across a 110 volt supply. Calculate; 5.1 the total resistance of the combination, 5.2 the current flow through each resistor,


(67,5 W; 45 V)


(5 A; 2,4 ohms)


(100,2 W; 110,1 V) (5,455 A; 40,33 ohms)


(24 ohms; 0,5 A)


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