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Set 300 Question Paper
Set 300
Course:Bachelor Of Science
Institution: Kenyatta University question papers
Exam Year:2010
KENYATTA UNIVERSITY
UNIVERSITY EXAMINATIONS 2010/2011
FIRST SEMESTER EXAMINATION FOR THE DEGREE OF BACHELOR OF
SCIENCE (ENERGY) AND BACHELOR SCIENCE (MANUFACTURING)
SET 300: ENGINEERING ELECTRONICS
DATE:
Wednesday 24th November 2010
TIME: 2.00p.m – 4.00p.m
INSTRUCTIONS:
? Attempt THREE questions.
? Question ONE is compulsory.
? Marks are shown in the parenthesis the end of each question.
Q1.
a)
Establish the relations
?
i)
? ?
[4marks]
1? ?
ii)
l ? ?l ? l
[8marks]
C
B
CEO
b)
A transistor is connected in common emitter configuration in which
collector supply is 8v and the voltage drop across collector resistance RC is
0.5V. The value of RC is 800 ? . If ? is 0.96, determine:
i)
Collector-emitter voltage (VCE)
ii)
Base current lB
[4marks]
c)
An npn transistor at room temperature has its emitter disconnected. A
voltage of 5V is applied between the collector and base. With collector
positive, a current of 0.2 ? A flows. When the base is disconnected and
the same voltage is applied between the collector and emitter, the current is
found to be 20 ? A. Find ?,l and l .
[10marks]
E
B
d)
Explain the significance of PIV as used with pn junction.
[1mark]
e)
State Three properties of semi-conductors.
[3marks]
Page 1 of 3
Q2.
a)
With the aid of diagrams, explain the operation of a transistor as an
amplifier.
[6marks]
b)
Draw a d.c load line for a transistor amplifier with the following values;
VCC = 12.5V, RC = 2.5 ? .
[3marks]
c)
Explain what is meant by the following terminologies as used in transistors?
i)
Cut-off region
ii)
Saturation region
iii)
Active region
[3marks]
d)
Describe the valence band, conduction band and forbidden energy gap with
the aid of energy level diagrams.
[6marks]
e)
Why are valence electrons of a material so important?
[2marks]
Q3.
a)
Explain the construction and operation of a thyristor using two transistor
analogy.
[10marks]
b)
With the aid of a clearly labeled diagram draw the equivalent circuit of a
Unijuction transistor (UjT) and show that intrinsic stand-off ratio is given
by;
R
1
B
? ?
[6marks]
R ? R
1
B
B2
c)
The intrinsic stand-off ration for a Unijuction transistor (UjT) is 0.6. If the
interbase resistance is 10k ? , what are the values of RB1 and RB2.
[4marks]
Q4.
a)
State the need for oscillators and mention some of its typical applications.
[3marks]
b)
With the aid of diagrams, explain the operation of tank circuit in an
oscillator.
[6marks]
c)
Find the capacitance of the capacitor required to build an LC oscillator that
uses an inductance of 1mH to produce a sine wave of frequency 1GHz.
[3marks]
d)
What is a pn junction? Explain the formation of potential barrier in a pn
junction.
[4marks]
Page 2 of 3
e)
With the aid of a diagram describe a half wave rectifier using a diode.
[4marks]
Q5.
a)
Draw a diagram of a zenor diode voltage stabilizer and explain how voltage
stabilization takes place.
[6marks]
b)
Find the output voltage EO, the voltage drop across resistor R and the
current through the zenor diode lZ given that, supply voltage is 120V,
R=5k ? , VZ=50V, and RL=10k ? .
[6marks]
c)
With the aid of diagrams, explain the following characteristics of a
transistor connected in common emitter.
i)
Input characteristic
ii
Output characteristic
[8marks]
Page 3 of 3
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