TUTORIAL 1 SEM 1 2022 Due Wed 23 March @10h00 QUESTION 1 Water is pumped to a height of 150 m at a rate of 300 litres per minute. The efficiencies of the pump and the 200 V driving motor are 73 % and 82 % respectively. Determine: a) The current of the motor b) The cost of running the motor for 14 hours per day (Note: 1kWh cost 35c) (6) (2) [8] QUESTION 2 Calculate the length of the resistor of a circular wire used in a heater element connected to a 240V supply and the heater consumes 8 joules of energy in 0,25 seconds. The resistor element is made of aluminium and it has a uniform cross-sectional area with a diameter of 0,00016 inches. Hints: 1inch = 25,4 mm, resistivity of aluminium = 2,825 x 10- 6 cm [8] QUESTION 3 A dc shunt motor after running for several hours on constant mains of 350 V takes a field current of 1,6 A. If the temperature rise is known to be 40°C, what value of extra circuit resistance is required to adjust the field current to 1,6 A when starting from cold at 20°C? The temperature coefficient of the motor’s armature material is 0,0043/K at 20°C. [5] QUESTION 4 4.1 Calculate the branch currents using Kirchoff law [7] 4.2 R2 IT = 2A + E 30V - R1 60 I3 Figure 8 R3 The questions below refer to figure above. a) Given that IT = 2A, find the total resistance RT. b) Show that IT is the sum of IR1, IR2 and IR3. c) Find IT. using the total supply (E) and RT. 60 (2) (5) (3) QUESTION 5 Determine the current through the 8 ohm resistor. 12 V 9Ω 8,5 Ω 2Ω 5Ω 7Ω 11 Ω 8Ω [12] Total Marks = 50 = 100%