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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: DECEMBER 2009 TIME: 2 HOURS
INSTRUCTIONS: Answer question ONE and any other TWO questions
QUESTION ONE
a) (i). State any FOUR applications of electrical energy.
(ii). Give your understanding and the units of each of the following parameters commonly
associated with electricity conduction:
?? Potential difference
?? Electrical current
?? Resistance
[8 Marks]
b) You are asked to measure the current through and voltage across resistor, say R. Show
diagrammatically how the appropriate measuring instruments would be connected to achieve your
objective. [4 Marks]
c) (i). Give a statement of Ohm’s Law
(ii). Show the Ohm’s Law graphically through an appropriate sketch, explaining the significance
of the gradient. [4 Marks]
2
d) A direct current (dc) power supply of electromotive force (emf), E, and internal resistance, r,
supplies power to two parallel-connected resistors whose resistances are R1 and R2.
(i). Show the above information in a circuit diagram, clearly indicating the direction of current flow
in all the branches.
(ii). Derive an expression of the equivalent resistance of the parallel-connected resistors R1 and R2.
[8 Marks]
e) Show, diagrammatically, the variation of the instantaneous current with time, i vs. t, in a direct
current RL circuit. [3 Marks]
f) The alternating current (ac) voltage in a domestic household in Kenya is 240 V. Determine:
(i). the maximum value of this voltage.
(ii). the direct current (dc) value
[3 Marks]
QUESTION TWO
a) Kirchhoff’s laws and the Superposition Theorem are often used to determine currents and voltages
in electrical circuits.
(i). Give statements of the two Kirchhoff’s Laws, and with the help of a circuit diagram, give
an equation of each.
(ii). Give a statement of the Superposition Theorem
[8 Marks]
b) Find the currents, I1, I2, and I3 shown in Fig. Q2 below. All resistors shown have their resistances
in ohms (O). Assume the 5V dc power supply has no internal resistance.
I1
I2 I3
A B C
F E D
5 V
3 10
7 8
[12 Marks]
QUESTION THREE
a) (i). Alternating current (ac) is almost the universal way of generating, transmitting and
distributing electrical power. Give reasons to support this.
3
(ii). Sketch the waveform showing the variation of voltage with time for an alternating current
(ac) power supply.
[4 Marks]
b) An alternating current (ac) circuit has a power supply of 220 V connected in series with a
resistance of 10O. For the circuit, determine the following:
(i). Root mean square (rms) current, maximum current, minimum current, and average current
(ii). the power consumed by the resistor
(iii). The power generated by the supply.
[9 Marks]
c) (i). Explain why a capacitor should never be charged by directly connecting it across a dc power
supply.
(ii). If a capacitor of value 1 µF and a resistor of value 10O are connected in series and a dc power
supply of value 20 V dc is connected across them, determine:
?? the time constant of the circuit;
?? the initial voltage across the capacitor;
?? the final voltage across the capacitor
[7 Marks]
QUESTION FOUR
a) A resistor is marked as follows:
?? 1st band – Brown,
?? 2nd band – Black,
?? 3rd band – Orange
?? 4th band – Silver.
Determine the following:
(i). standard value of resistance;
(ii). minimum value of resistance;
(iii). maximum value of resistance.
[9 Marks]
b) Define the resistivity of a resistor and show its units. [3 Marks]
4
c) Three resistors (R1, R2 and R3) made from the same material have dimensions shown in Table Q4.
Table Q4. Resistance dimensions
R1 R2 R3
Crosssectional
area
A A 2A
Length l 2l l
The current through resistor R1 is 10 A for a given voltage V. For the same voltage separately applied
across R2 and R3, determine the currents flowing.
[8 Marks]
QUESTION FIVE
An electrical coil has an inductance of 2 mH and a resistance of 3O. The coil is connected in parallel
with a capacitor of 40 uF. A 10 V, 400 Hz ac supply is then connected across the combination.
a) Give a sketch of the electrical circuit and present all the information on the circuit.
[5 Marks]
b) Determine:
(i) The periodic time of the supply waveform
(ii) The time constant associated with the RL branch only
(iii) The current magnitude in the capacitive branch.
(iv) The current magnitude in the RL branch.
[15 Marks]

Basic Electricity Question Paper

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