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%