UNIVERSITY OF MINES AND TECHNOLOGY, TARKWA
SECOND SEMESTER EXAMINATIONS, MAY 2015
COURSE NO : EL/MC/PE/CE 164
COURSE NAME: BASIC ELECTRONICS
CLASS : BSc I TIME: 3 HOURS
Name: …………………………………………………Index Number: …………………………..
INSTRUCTION: ANSWER ALL QUESTIONS
SECTION A [20 Marks]
Choose the appropriate letter that corresponds with the correct answer
1. The current gain of a bipolar transistor used in Common Collector (emitter follower) mode will be:
A. About 50 to 100 B. About 50 to 800
C. 1 (Unity) D. Several thousand
2. To increase the number of free electrons in silicon for use in transistors, manufacturers add small amounts
of:
A. Germanium B. Aluminium
C. Boron D. Arsenic
3. A bipolar transistor has _________.
A. Three P-N junctions. B. Three semiconductor layers.
C. Two N-type layers around a P-type layer. D. A low avalanche voltage.
4. When a transistor is conducting as much as it possibly can, it is said to be_______.
A. In cutoff. B. In saturation.
C. Forward biased. D. In avalanche.
5. The greatest possible amplification is obtained in:
A. A common-emitter circuit. B. A common-base circuit.
C. A common-collector circuit. D. More than one of the above.
6. In a bipolar junction transistor the input is applied to the collector in:
A. A common-emitter circuit. B. A common-base circuit.
C. A common-collector circuit. D. None of the above.
7. In a common-base circuit, the output is taken from the:
A. Emitter. B. Base.
C. Collector. D. More than one of the above.
8. The current through the channel of a JFET is directly affected by all of the following except:
A. Drain voltage. B. Transconductance.
C. Gate voltage. D. Gate bias.
9. In an N-channel JFET, pinchoff occurs when the gate bias is ______________.
A. Slightly positive. B. Zero.
C. Slightly negative. D. Very negative.
Page 1 of 3
10. The current consists mainly of holes when a JFET __________ .
A. Has a P-type channel. B. Is forward-biased.
C. Is zero-biased. D. Is reverse-biased.
SECTION B [30 Marks]
State whether the statement is True or False
Q Statement True/False
1 All are diodes; 2N4001, 1N4148, 1N4147, 1N3038 and 1N4007
2 Gallium Asenide(GaAs) is an example of elemental semiconductor.
3 All these circuits-clamper, clipper, multiplier, regulator use rectifier diodes.
4 LED can switch on and off at a much faster rate than rectifier diode.
5 Zener diodes are designed to operate and be used in forward direction only.
6 Passive filters do require external power supply, like active filters, to operate.
The resonant effect is used to build filters that pass or reject certain
7
frequency bands.
8 A low pass filter uses inductor in parallel with the load.
9 The output of a rectifier diode results in a pulsating dc.
10 In the reversed direction, rectifier diodes are like closed circuit.
11 The bipolar junction transistor (BJT) is a voltage control device.
12 Gate bias is the best way to bias JFETs.
Transconductance curve of JFET is graph of drain current (ID) versus gate-
13
to-source voltage (VGS).
The maximum value of the reverse voltage that can be continually applied to
14 the rectifier diode before breakdown is known as Steady state reverse
voltage.
15 FETs are voltage control devices.
Page 2 of 3
SECTION C [50 Marks]
Question 1
(a) What is Rectification? [2 Marks]
(b) State three differences between a rectifier diode and zener diode? [3 Marks]
(c) Explain what is meant by the term pulsating DC? [5 Marks]
(d) Draw the circuit and the expected output waveform of a regulated DC power supply consisting of the
following: A 240-volt single phase AC supply; A 240/24 –volts transformer; A Bridge Rectifier;
choke input passive low-pass filter; LM 7918 IC Regulator and 2 kΩ Load Resistor. [10 Marks]
Question 2
(a) What is meant by pinch-off voltage as applied to Junction Field Effect Transistors (JFETs)?
[5 Marks]
(b) State five differences between Bipolar Junction Transistors (BJTs) and Field Effect Transistors
(FETs). [5 Marks]
(c) With diagrams only, differentiate between N-channel JFET and N-channel Depletion MOSFET in
terms of; Material Construction, Schematic symbol, and I-V characteristics. [10 Marks]
(d) Draw the DC load line of the circuit in Figure 1 and show the values of IC(Sat), VCE(Off), ICQ and VCEQ.
Assume VBE to be 0.7 V. [10 Marks]
Examiner: P. Blewushie
Page 3 of 3
