Solved Model Question Paper:Basics of Electronics Engineering EC100

Basics of Electronics Engineering EC100

Model Question Paper with Answers


1. Differentiate relays and contactors and write the applications of each.

Relay Contactor

  • Relatively smaller in size.

  • Larger when compared to relays.

  • Used in circuits with lower ampacity. (Max 20A)

  • Used in circuits with low and higher ampacity up to 12500A.

  • Mainly used in control and automation circuits, protection circuits and for switching small electronic circuits

  • Used in the switching of motors, capacitors, lights etc.

  • Consists of at least two NO/NC contacts.

  • Consists of minimum one set of three phase power contacts and in some cases additional auxiliary contacts are also provided.

2. What is tolerance of a resistor? Find the resistance range for the carbon resistor
having the colour bands: yellow, violet, red and gold.
Tolerance is the percentage of error in the resistor's resistance, or how much more or less
you can expect a resistor's actual measured resistance to be from its stated resistance. A
gold tolerance band is 5% tolerance, silver is 10%, and no band at all would mean a 20%
Resistance range of the given color band is 4.7K  5%.

3. Write any four applications of electronics in the field of defense.

  • Electronic circuits provide a means of secret communication between the headquarter

and different units

  • RADAR that is Radio Detection and Ranging is the most important development in

electronics field. With the help of radar, it is possible to detect and find the exact
location of enemy aircraft, Radar and anti-craft guns can be linked by an automatic
control system to make a complete unit

  • Circuit boards and sub-assemblies for military firing simulators (anti-tank)
  • Electrical distribution circuit boards for military helicopters

4. Draw the energy band diagrams of insulator, semiconductor and conductor.

5. How does an Avalanche breakdown differ from Zener break down?
Zener break down
Avalanche breakdown
1.This occurs at junctions, which being
heavily doped have narrow depletion
1. This occurs at junctions which being
lightly doped has wide depletion layers.
2. This breakdown voltage sets a very
strong electric field across this narrow
2. Here, electric field is not strong
enough to produce Zener breakdown.
3. Here, electric field is very strong to
rupture the covalent bonds thereby
generating electron hole pairs. So even
a small increase in reverse voltage is
capable of producing large number of
current carriers, i.e. why the junction
has a very low resistance. This leads to
Zener breakdown
3. Here, minority carriers collide with
semiconductor atoms in the depletion
region, which breaks the covalent
bonds and electron-hole pairs are
generated. Newly generated charge
carriers are accelerated by the electric
field, which results in more collision
and generates avalanche of charge
carriers. This results in avalanche

6. Write the type number of the following:
a) Low frequency low power transistor,
b)High frequency low power transistor, c) Power Transistor, d) Rectifier Diode.

Low frequency low power transistor= AC540
High frequency low power transistor=AF125
Power Transistor=TO220
Rectifier Diode
50 V
1 A
100 V
1 A
200 V
1 A
400 V
1 A
600 V
1 A
800 V
1 A
1,000 V
1 A

7. What is the working principle of SMPS?
SMPS means switch mode power supply. This works on the principle of switching
regulation. The SMPS system is highly reliable, efficient, noiseless and compact because the
switching is done at very high rate, in the order of several KHz to MHz.

8. Describe the role of different capacitors in RC coupled amplifier.
  • Coupling capacitor CC is used to connect the output of first stage to the base, i.e.
input of the second stage and this continues when more stages are connected. The
coupling capacitor CC transmits AC signal but blocks DC. This prevents DC
interference between various stages and the shifting of operating point.
  • The emitter bypass capacitor offers a low resistance path to the signal. Without this
capacitor the voltage gain of each stage would be lost.

9. Define bandwidth of an amplifier and mark the important parameters in the
frequency response graph.

The bandwidth (BW) of an amplifier is the difference between the frequency limits of the
amplifier, the bandwidth represents the amount or "width" of frequencies, or the "band of
frequencies," that the amplifier is MOST effective in amplifying. However, the bandwidth is
NOT the same as the band of frequencies that is amplified.
Frequency response graph
10. Draw the internal block diagram of op-amp and write the functions of each block.
Input stage: It consists of a dual input, balanced output differential amplifier. Its function is
to amplify the difference between the two input signals. It provides high differential gain,
high input impedance and low output impedance.

Intermediate stage: The overall gain requirement of an Op-Amp is very high. Since the
input stage alone cannot provide such a high gain. Intermediate stage is used to provide the
required additional voltage gain.
It consists of another differential amplifier with dual input, and unbalanced (single ended)

Buffer and Level shifting stage
As the Op-Amp amplifies D.C signals also, the small D.C. quiescent voltage level of previous
stages may get amplified and get applied, as the input to the next stage causing distortion to
the final output.
Hence, the level shifting stage is used to bring down the D.C. level to ground potential,
when no signal is applied at the input terminals. Buffer is usually an emitter follower used
for impedance matching.

Output stage- It consists of a push-pull complementary amplifier, which provides large
A.C. output voltage swing and high current sourcing and sinking along with low output

11. Realize the logic functions: Sum S= A+B and Carry CY =AB using gates and prepare
the truth table
Truth table:

A B SUM(S)=A+B Carry(CY)=AB
0 0 0 0
0 1 1 0
1 0 1 0
1 1 1 1
12. What are the advantages of integrated circuits?
                       1. Extremely small size – thousand times smaller than discrete circuits. It is because of
fabrication of various circuit elements in a single chip of semiconductor material.
                      2. Very small weight owing to miniaturized circuit.
                      3. Very low cost because of simultaneous production of hundreds of similar circuits on a small semiconductor wafer. Owing to mass production of an IC costs as much as an individual transistor.
                     4. More reliable because of elimination of soldered joints and need for fewer interconnections.
                     5. Lower power consumption because of their smaller size.
13. What is frequency modulation? Write the frequency bands used for AM and FM

Frequency modulation
It is a process in which the frequency of the carrier is varied in accordance with the
instantaneous value of modulating or information signal.

Frequency bands used for AM and FM broadcast.
The Amplitude Modulated (AM radio) carrier frequencies are in the frequency range
535-1605 kHz. Carrier frequencies of 540 to 1600 kHz are assigned at 10 kHz intervals.
The FM radio band is from 88 to 108 MHz between VHF televisions. The FM stations are
assigned center frequencies at 200 kHz separation starting at 88.1 MHz, for a maximum of
100 stations. These FM stations have a 75 kHz maximum deviation from the center
frequency, which leaves 25 kHz upper and lower "gaurd bands" to minimize interaction
with the adjacent frequency band.

14. Write the RADAR range equation and list the factors affecting the range.
Maximum RADAR range equation is
List the factors affecting the range
                1. The maximum range at which it can see a target of a specified size.
                2. The accuracy of its measurement of target location in range and angle.
                3. The ability to distinguish one target from another.

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