NATIONAL OPEN UNIVERSITY OF NIGERIA
14/16 AHMADU BELLO WAY, VICTORIA ISLAND, LAGOS
SCHOOL OF SCIENCE AND TECHNOLOGY
MARCH/APRIL 2014 EXAMINATION
COURSE CODE: PHY 364
COURSE TITLE: ELECTRONICS II
TIME ALLOWED:
INSTRUCTION: ANSWER QUESTION ANY FIVE QUESTIONS
QUESTIONS ONE
a. Figure 1 shows the circuit diagram for a simple d.c. power supply. Identify the type of rectifier circuit represented in figure 1 and explain the operation of the circuit with reference to the function of each component within the circuit.
b. The transformer is connected to a 220 V rms mains supply at 50 Hz and has a step-down turns ratio of 10:1. Calculate the peak secondary voltage from the transformer.
c. The power supply unit shown in figure 1 is said to be unregulated – Explain the meaning of the term unregulated as used in relation to power supplies.
QUESTIONS TWO
a. The figure below show how a three terminal regulator chip may be used to provide a regulated output voltage.
i. How can a better result be achieved in terms of rectification.(Hint: consider the different rectifiers)
ii. In relation to power supply units, explain the meaning of the terms percentage load regulation.
b. Differentiate between FET and BJT transistors.
QUESTIONS THREE
a.
i. List the three major advantages and one major disadvantage active filters have over passive filters?
ii. Understand the Q factor of a filter
iii. Describe the various ways of generating electrical energy
b. Sketch an electrical power distribution system
QUESTIONS FOUR
a.
i. Explain the operation of a hum injector filter and state its major advantage in its specialized application?
ii. Complete table 1 of output voltages, output currents, and input currents for several given values of input voltage in this common-collector amplifier circuit. Assume that the transistor is a standard silicon NPN unit, with a nominal base-emitter junction forward voltage of 0.7 volts:
QUESTIONS FIVE
a. What are the four classifications of switched mode power supplies? State a practical application of each class?
b. With reference to the circuit in figure 9(a), explain the likely consequences for the light emitting diode (LED) of closing the switch. (NB the forward biased LED exhibit a forward voltage of 2 V)
c.
i. Calculate an approximate value for the current flowing in the LED.
QUESTIONS SIX
a.
i. How can you reduce signal distortion in amplifier
ii. Explain the function of biasing diodes in a class B bipolar transistor amplifier?
iii. Each diode in a center-tapped full-wave rectifier is _____ -biased and conducts for _____ of the input cycle.
b.
i. The transistor amplifier that provides the greatest input impedance is known as?
c.
The probable trouble, if any, indicated by these voltages is:
QUESTIONS SEVEN
a.
i. The output frequency of a half-wave rectifier is _____ the input frequency.
ii. If the ac supply is 60 Hz, what will be the ripple frequency out of the half-wave rectifier? If the ac supply is 50 Hz, what will be the ripple frequency out of the full-wave rectifier?
iii. Explain the correct relationship between emitter, base and collector currents?
b.
i. Refer to the given figure 11. This circuit is known as a ________ filter, and the fc is ________.
You can get the exam summary answers for this course from 08039407882
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