Get premium membership and access revision papers, questions with answers as well as video lessons.

Got a question or eager to learn? Discover limitless learning on WhatsApp now - Start Now!

Basic Electricity Question Paper

Basic Electricity

Course:Bachelor Of Science In Information Technology

Institution: Kca University question papers

Exam Year:2009

UNIVERSITY EXAMINATIONS: 2009/2010
FIRST YEAR EXAMINATION FOR THE DEGREE OF BACHELOR OF
SCIENCE IN INFORMATION TECHNOLOGY
BIT 1103: BASIC ELECTRICITY
DATE: APRIL 2010 TIME: 2 HOURS
INSTRUCTIONS: Answer question ONE and any other TWO questions
Question One
a) (i).Justify the following statement:
“The welfare and overall security of a modern society
will be totally compromised in the absence of
electricity”.
[3 Marks]
(ii). State the main components of a basic electrical circuit and give a diagrammatic representation of
such a circuit. [5 Marks]
(iii). State the role of a fuse in an electrical circuit. [2 Marks]
b) A resistor is one of the common components in an electrical circuit and often dissipates energy in
the form of heat when a current flows through the resistor.
i. Explain the meaning of the phrase “power rating” as used in reference to resistors[2 Marks]
ii. Define the term “resistivity” when used with reference to resistors and give the units of this
parameter. [3 Marks]
iii. A resistor is marked as follows: 1st band – Brown, 2nd band – Black, 3rd band – Orange and
the 4th band – Silver. If this resistor is rated at 4
1 watt, determine the maximum rated
current and voltage that can be passed through it and applied across it respectively.
[5 Marks]
c) In working with electrical circuits, it is necessary to determine the current flowing through a circuit
components as well as the potential drop across the component.
i. State the names of the meters used to measure current and potential drop. [2
Marks]
ii. Identify the fundamental property of each meter mentioned in c(i) which should enable the meter to accurately measure the parameter it is supposed to measure. [4 Marks]
iii. An ammeter is connected in parallel with a circuit component whose current is to be
measured while a voltmeter is connected in series with a circuit component whose voltage
is to be measured. Explain what will happen and propose an alternative arrangement of the
two meters to respectively measure current and voltage. [4 Marks]
Question Two
a) A load resistance, RL, draws a current, IL, and in the process consumes an amount of power, PL. For
varying values of RL, the corresponding values of IL and PL are captured in Table Q2. The direct current (dc) power supply has an equivalent voltage (VTH) and internal resistance (RTH).
Table Q2. Variation of resistance RL, current and power delivered in RL
Load resistance RL (ohms) Load Current, IL (A) Load Power, PL (W)
i) Draw an electric circuit diagram of the dc series circuit described. [4 Marks]
ii) From Table Q2, determine the value of:
• Load resistance (RL) at which maximum power is consumed by the load;
• Load current when maximum power is consumed by the load [2 Marks]
iii) According to Thevenin Theorem, the power consumed by a load is maximum when the
load resistance (at maximum power consumption) is equal to the Thevenin equivalent
resistance of the supply. Determine the Thevenin resistance of the supply (RTH). [2 Marks]
iv) From the sketch of the dc series circuit in (i), determine the equation for load current (IL) in
terms of supply voltage (VTH), Thevenin resistance of the supply (RTH) and load resistance
(RL). [2 Marks]
v) Given the values (as determined above and also shown in Table Q2) of RL at maximum
power consumption, IL at maximum power consumption and RTH, determine the supply
voltage (VTH). [3 Marks]
vi) Hence determine the load current and power consumed when the load resistance RL is 20
ohms. [5 Marks]
vii) Sketch the variation of load resistance with load power for values of load resistance
between 5O and 20 O. [2 Marks]
Question Three
a) State Ohm’s Law, and graphically represent the same as a sketch [4 Marks]
b) Show, from basic principles, that the equivalent resistance (Req) of two resistors R1 and R2
connected in parallel can be given by the expression below (i.e., product of the resistors divided by
their sum):
Req = R1R2/(R1 + R2) [5 Marks]
c) Briefly explain why electrical power is generated, transmitted and distributed almost universally in
alternating (ac) form and not direct (dc) form? [2 Marks]
d) (i). Give statements of the Superposition Principle
(ii). Demonstrate your understanding of the Superposition Theorem by using it to determine thecurrent in the 10O resistor in Fig. 3.
[9 Marks]
Question Four
An RL circuit is shown in Fig. 4, where the dc voltage, V, is applied at time zero by closing the switch
(S). Assume zero initial conditions (i=0 at t=0) and exponential growth. For the circuit, V is 15V, L is
5 H and R is 2O.
R i L
a) Sketch a diagram showing the variation of the instantaneous current with time, i vs. t, in a direct
current (dc) RL circuit. [3 Marks]
b) State the expression for the current flowing (i.e., current growth equation) at any time instant, t,
when the switch S is close. [3 Marks]
c) Find the time constant of the circuit. [4 Marks]
d) If the switch is suddenly closed (at t = 0), find the final current in the circuit. [4 Marks]
e) A short circuit is placed across the coil when the final steady state current is flowing. Find the
current after 2.5 seconds. [6 Marks]
Question Five
a) On three different sketches, show the phase relationship between the current and voltage
waveforms under the following conditions: Define the following terms:
i. AC Voltage applied across a pure inductor
ii. AC Voltage applied across a pure capacitor
iii. AC Voltage applied across a resistor [6 Marks]
b) A coil of inductance 2 mH and resistance 3 ohms is in parallel with a 40 uF capacitor. They are
connected to a 10 V, 400 Hz ac supply.
i. Give a sketch of the electrical circuit and present all the information on the circuit.
ii. Determine:
• the current magnitude in the capacitive branch.
• the current magnitude in the RL branch [14 Marks]

Basic Electricity Question Paper

More Question Papers

Popular Exams