lab viva

1. ELECTRONICS VIVA QUESTIONS WITH ANSWERS
1. What is electronic?
The study and use of electrical devices that operate by controlling the flow of electrons or
other electrically charged particles.
2. What is engineering?
The application of science to the needs of humanity and a profession in which a
knowledge of the mathematical and natural sciences gained by study, experience, and practice is
applied with judgment to develop ways to use economically the materials and forces of nature
for the benefit of mankind.
3. Difference between electronic and electrical?
Electronics work on DC and with a voltage range of -48vDC to +48vDC. If the electronic
device is plugged into a standard wall outlet, there will be a transformer inside which will
convert the AC voltage you are supplying to the required DC voltage needed by the device.
Examples: Computer, radio, T.V, etc...
Electric devices use line voltage (120vAC, 240vAC, etc...). Electric devices can also be
designed to operate on DC sources, but will be at DC voltages above 48v. Examples are
incandescent lights, heaters, fridge, stove, etc...
4. Semiconductors?
Semiconductors are partial conductors which conducts electricity partially through them.
They play major role in electronics.
1 P-N Junction diode
2. Zener diode
5. Define diode and its property?
A diode is a two-terminal electronic component with asymmetric conductance, it has low
(ideally zero) resistance to current flow in one direction, and high (ideally infinite) resistance in
the other. A diode is an electronic device that allows current to flow through it in one direction
only.

2. 6. What are the different types of diodes?
a) Small signal diodes,
b) Rectifiers (power) diodes (e.g. in power supplies),
c) Switching diodes,
d) Zener diodes,
e) Light Emitting Diodes (LED).
7. What is PN junction diode?
A solid-state photosensitive device with a junction between a p-type and an n-type
semiconducting material. In the target of a SIT tube, a tightly spaced, fine matrix of p-n junction
diodes are formed on a very thin wafer of silicon. They amplify the photoelectrons generated in
the intensifier section.
8. What is meant by biasing a PN junction?
Connecting a PN junction to an external voltage source is biasing a PN junction.
9. What are the types of biasing a PN junction?
1. Forward bias
2. Reverse bias.
10. What is forward bias in a PN junction?
When positive terminal of the external supply is connected to P region and negative
terminal to N region, the PN junction is said to be forward biased. Under forward biased
condition the PN region offers a very low resistance and a large amount of current flows through
it.
11. What is reverse bias in a PN junction?
When positive terminal of the external supply is connected to N type and negative
terminal to P type then the PN junction is said to be in reverse bias. Under reverse biased
condition the PN region offers a very high resistance and a small amount of current flows
through it.

3. 12. Define potential barrier. What is a potential barrier for Si and Ge?
A restraining force due to which the diffusion of majority carriers is stopped from one
side to another side is called barrier potential. (Or) The oppositely charged ions present on both
sides of PN junction an electric potential is established across the junction even without any
external voltage source which is termed as barrier potential.
Potential barrier of Si = 0.6V
Potential barrier of Ge = 0.2V
13. P-N Junction Diode Characteristics?
Forward and Reverse Characteristics of a Diode: The response of a diode can be easily
indicated using the characteristics which called as V-I characteristics of diode.
14. What is depletion region in PN junction?
The region around the junction from which the mobile charge carriers (electrons and
holes) are depleted is called as depletion region. Since this region has immobile ions, which are
electrically charged, the depletion region is also known as space charge region.

4. 15. What is the effect of forward biasing on the width of depletion region and the barrier
potential?
Width of the depletion region decreases with increase in forward biasing and the barrier
also decreases.
16. What is the effect on barrier potential on forward biased PN junction?
Barrier potential decreases with increase in forward biasing.
17. Why does the width of depletion region increases with increase in reverse biasing?
When a PN junction is reversed biased, the holes in the P region are attracted towards the
negative terminal of the voltage source and the electrons in the N region are attracted towards
positive terminal of the voltage source. This widens the depletion layer and increases the barrier
potential.
18. Define reverse saturation current?
In reverse biased PN junction practically no current flows due to majority carriers. A
small amount of current does flow due to the diffusion of minority carriers which are the hole
electron pairs generated through pout the semi- conductor material as a result of thermal energy.
The current so produced is known as reverse saturation current.
19. What are the types of reverse breakdown occurring in a PN junction diode?
1. Zener breakdown
2. Avalanche breakdown
20. What do you mean by zener breakdown?
In this case, the breakdown down occurs in junctions, which are heavily doped. The
heavily doped junction has a narrow depletion region. When the reverse voltage is increased, the
electric field at the junction also increases. A strong electric field causes covalent bond crystal
structure. As a result of this is large no of minority carriers are generated and a large current
flows through the junction.

5. 21. Explain the phenomenon of avalanche breakdown?
In this case the increased voltage increases the amount of energy imparted to minority
carriers as they diffuse across the junction. As the reverse voltage is increased, further the
minority carriers acquire a large amount of energy. When these carriers collide with silicon
atoms, within the crystal structure they impart sufficient energy to break a covalent bond and
generate additional carriers. These additional carriers pick up energy from the applied voltage
and generate still more carriers. As a result of this the reverse current increases rapidly. This
cumulative process of carrier generation is known as avalanche break down.
22. What is the type of capacitance which exists in a PN junction under forward biased
condition?
Diffusion or storage capacitance.
23. What is the type of capacitance which exists in a PN junction under reverse biased
condition?
Junction capacitance/ depletion / space charge capacitance
24. Explain the effect of temperature on diode characteristic?
With increase in temperature the exponent will reduce and diode current will also
decrease.
25. What is the static resistance of a diode?
Static resistance R of a diode can be defined as the ratio of voltage V across the diode to
the current flowing through the diode.
R = V/ I Where, R - Static resistance of a diode
V - Voltage across the diode
I - current across the diode
26. Define dynamic resistance.
Dynamic resistance of a diode can be defined as the ratio of change in voltage across the
diode to the change in current through the diode.
r = V / I
Where, r - Dynamic resistance of a diode
V - change in voltage across the diode
I - change in current through the diode

6. 27. What is rectifier?
A rectifier is an electrical device that converts alternating current (AC), which
periodically reverses direction, to direct current (DC), which flows in only one direction. The
process is known as rectification.
28. What is transformer?
A transformer is a static electrical device that transfers energy by inductive coupling
between its winding circuits. Transformers are essential for the transmission, distribution, and
utilization of electrical energy.
29. What happen when Transformer is given DC supply?
When DC supply is given to the transformer primary winding no back emf is induced in
the transformer. Importance of Back emf is that it limits the current drawn by the machine. In the
absence of back emf transformer starts drawing huge currents which results in burning down of
primary winding. So when dc supply is given to transformer primary windings will burn.
30. What is ripple factor?
Ripple factor (γ) may be defined as the ratio of the root mean square (rms) value of the
ripple voltage to the absolute value of the dc component of the output voltage, usually expressed
as a percentage. However, ripple voltage is also commonly expressed as the peak-to-peak value.
31. Write the formula for ripple factor for a half wave rectifier?
Theoretical calculations for Ripple factor:-
Without Filter:
Vrms= Vm/2, Vdc= Vm/
Ripple factor =
With Filter:
Where, f = 50Hz and R = 1K

7. 32. What is efficiency?
Rectifier efficiency is the ratio of the DC output power to the AC input power.
33. What is PIV?
The peak inverse voltage is either the specified maximum voltage that
a diode rectifier can block, or, alternatively, the maximum that a rectifier needs to block in a
given application.
34. What are the applications of rectifier?
The primary application of rectifiers is to derive DC power from an AC supply. Virtually
all electronic devices require DC, so rectifiers are used inside the power supplies of virtually all
electronic equipment. Rectifiers are also used for detection of amplitude modulated radio signals.
Rectifiers are used to supply polarized voltage for welding.
35. What is the function of the filters?
36. What is TUF?
38. What is the efficiency of half wave rectifier?
39. What is logic gate?
A logic gate is an idealized or physical device implementing a Boolean function, that is,
it performs a logical operation on one or more logical inputs, and produces a single logical
output.

8. 40. What are Universal gates? Why are they call so?
NAND and NOR gates called universal gates. All other gates/functions can be
implemented by NOR or NAND gates. So they are called universal gates.
41. Define Flipflop?
The basic unit for storage is flip flop. A flip-flop maintains its output state either at 1 or 0
until directed by an input signal to change its state.
42. State De Morgan's theorem?
De Morgan suggested two theorems that form important part of Boolean algebra. They are
1) The complement of a product is equal to the sum of the complements. (AB)' = A' + B'
2) The complement of a sum term is equal to the product of the complements. (A + B)' =
A'B'
43. Explain Kirchhoff’s law?
Kirchhoff's circuit laws are two approximate equalities that deal with the current and
potential difference (commonly known as voltage) in electrical circuits.
Kirchhoff’s Current Law (KCL):
This law is also called Kirchhoff's first law, Kirchhoff's point rule, or Kirchhoff's
junction rule (or nodal rule).
The principle of conservation of electric charge implies that:
 At any node (junction) in an electrical circuit, the sum of currents flowing into
that node is equal to the sum of currents flowing out of that node, or:
 The algebraic sum of currents in a network of conductors meeting at a point is
zero.
 The current entering any junction is equal to the current leaving that
junction. i2 +i3 = i1 + i4
Kirchhoff’s Voltage Law (KVL):
This law is also called Kirchhoff's second law, Kirchhoff's loop (or mesh) rule, and
Kirchhoff's second rule. The sum of all the voltages around the loop is equal to zero.
v1 + v2 + v3 - v4 = 0.

9. 44. What is CRO?
The cathode-ray oscilloscope (CRO) is a common laboratory instrument that provides
accurate time and amplitude measurements of voltage signals over a wide range of frequencies.
C.R.O is a versatile instrument used for display of wave forms and is a fast x-y plotter.
The heart of C.R.O is and the rest is the circuitry to operate C.R.O
45. What are the main parts of CRO?
1. Electron gun: - it is used to produce sharply focused beam of electron accelerated to
very high velocity.
2. Deflection system: - it deflects the electron both in horizontal and vertical plan.
3. Florescent screen:- the screen which produces, spot of visible light . when beam of
electrons are incident on it the other side of tube is coated with phosphorus material.
46. Front Panels of CRO
 ON-POWER: toggle switch for switching on power.
 INTENCITY: controls trace intensity from zero to maximum.
 FOCUS: It controls sharpness of trace a slight adugestement of focus is done after
changing intensity of trace.
 AC-DC: GROUND: It selects coupling of AC-DC ground signal to vertical amplifier.
 X-MAG: It expands length of time base from 1-5 times continuously and to maximum
time base to 40 ns/cm.
 SQUARE: This provides square wave 2v (p-P) amplitude and enables to check y
calibration of scope.
 SAWTOOTH WAVE FORM: This provides saw tooth wave form output coincident to
sweep speed with an output of saw tooth wave (p-p)
 VERTICAL SECTION: y position: This enables movement of display along y-axis.
 Y-INPUT: It connects input signal to vertical amplifier through AC-DC ground
coupling switch

10.  CALIBRATION: 15mv – 150mv dc signal depending on position selection is applied to
vertical amplifier.
 DC BALANCE: It is control on panel electrostatic ally in accordance with waveforms
to be displayed.
 VOLTS/CM: Switch adjusts sensitivity.
 HORIZANTAL SECTION: X-POSITION: This control enables movement of display
along x-axis.
 TRIGGERING LEVEL: It selects mode of triggering.TIMEBASE: This controls or
selects sweep speeds.
 VERNUIS: This control the fine adjustments associated with time base sweep.
 SIGN SELECTOR: It selects different options of INT/EXT, NORM/TO.
 STAB: Present on panel
 EXITCAD: It allows time base range to be extended.
 HORIZANTAL INPUT: It connects external signal to horizontal amplifier.
 Ext SYN: it connects external signal to trigger circuit for synchronization.
47. Observations of CRO:
Amplitude = no. of vertical divisions * Volts/div.
Time period = no. of horizontal divisions * Time/div.
Frequency=1/T
Amplitude taken on vertical section (y).
Time period taken on horizontal section(x)
48. Applications of CRO:
1. Measurement of current
2. Measurement of voltage
3. Measurement of power

11. 4. Measurement of frequency
5. Measurement of phase angle
6. To see transistor curves
7. To trace and measuring signals of RF, IF and AF in radio and TV.
8. To trace visual display of sine waves.
49. What is a Function Generator?
A function generator is usually a piece of electronic test equipment or software used to
generate different types of electrical waveforms over a wide range of frequencies. Some of the
most common waveforms produced by the function generator are the sine, square, triangular and
sawtooth shapes. Function generators are used in the development, test and repair of electronic
equipment.
Designation Specifications
Wave form : Sine, squares, triangles, TTL square waves
Amplitude : 0-20V for all the functions.
Sine distortion : Less than 1% from 0.1 HZ to 100 HZ harmonics
Modulation showed down fundamental for 100k
HZ to 1MHZ.
Offset : Continuously variable 10V
Frequency range : 0.1 HZ to 3Μhz in ranges.
Output impedance : 600 ohms, 5%.
Square wave duty cycle : 49% to 51%.

12. Differential linearity : 0.5%
Range selectors: Decode frequency by multiplying the range selected with the frequency
indicated by dial gives the output frequency, which applies for all functions.
Function selectors: Selected desired output wave form which appears at 600Ω output.
VCO input: An external input will vary the output frequency. The change in frequency is
directly proportional to input voltage.
TTL output: A TTL square wave is available at this jack. The frequency is determined by the
range selected and the setting of frequency dial. This output is independent of amplitude and
D.C OFFSET controls.
Amplitude control: Control he amplitude of the output signal, which appears at 600ohms.
OFFSET control: Control the DC offset of the output. It is continuously variable for ±5V,
±100V.
Fine frequency dial: Multiplying the setting of this dial to the frequency range selected gives
the output frequency of the wave forms at the 600ohms.
50. What is Regulated Power Supply?
Power supplies provided by a regulated DC voltage facilities fine and coarse
adjustments and monitoring facilities for voltage and current. They will work in constant
voltage and current mode depending on current limit and output load.
The current limit has good stability, load and line regulations. Outputs are protected
against overload and short circuit damages. They are available in single and dual channel
models with different voltage and current capacities. Overload protection circuit of constant
self restoring type is provided to prevent the unit as well as the circuit under use.
The power supplies are specially designed and developed for well regulated DC output.
These are useful for high regulation laboratory power supplies, particularly suitable for
experimental setup and circuit development in R&D.
51. Define ohm’s law?
Ohm's law states that the current through a conductor between two points is directly
proportional to the potential difference across the two points.

13. where I is the current through the conductor in units of amperes, V is the potential difference
measured across the conductor in units of volts, and R is the resistance of the conductor in
units of ohms.
Ohm's law states that the voltage (V) across a resistor is proportional to the current (I), where the
constant of proportionality is the resistance (R).
52. What is a Resistor?
An electric resistor is a two-terminal passive component specifically used to oppose and
limit current. A resistor works on the principle of Ohm’s Law which states that voltage across
the terminals of a resistor is directly proportional to the current flowing through it.
The unit of resistance is ohms.
54. Explain the colour coding of resistors?
. The measuring digits against color codes given in the following table. The sentence within the
quotation marks may be of great help to memorize these color codes in order, "B.B. ROY of
Great Britain has a Very Good Wife".

14. COLOR First digit for
the 1st
band
Second digit
for the 2nd
band
Multiplier
digit for the
3rd
band
Resistance
tolerance
Black 0 0 10^0 -
Brown 1 1 10^1 ±1%
Red 2 2 10^2 ±2%
Orange 3 3 10^3 ±3%
Yellow 4 4 10^4 -
Green 5 5 10^5 -
Blue 6 6 10^6 -
Violet 7 7 10^7 -
Gray 8 8 10^8 -
White 9 9 10^9 -
Gold - - 10^-1 ±5%
Silver - - 10^-2 ±10%
No color - - - ±20%
E.g. the value of a four band Carbon resistor having color bands Red, Red, Red, Silver
will have value 22*100=2200 Ohms with 10% tolerance.
54. What are the types of resistors?

15. Resistors can be broadly classified based on the following criteria: the type of material
used, the power rating and resistance value.
1. Fixed resistor
2. Variable resistors
55. What is Capacitor?
Capacitors are used to store large amount of static current. When they are included in
circuit it acts open circuit. Capacitors are widely used in electronic circuits for blocking direct
current while allowing alternating current to pass. SI unit of capacitance is the farad, which is
equal to one coulomb per volt.
They are three types
1. Disk capacitor
2. Fixed capacitor
3. Variable capacitor
56. What is Inductor?
The inductance is defined as the ability of an inductor which opposes the change in
current. It is denoted by the letter “L” and its unit is Henry(H). They are used to block the flow
of AC current while allowing DC to pass; inductors designed for this purpose are called chokes.
57. What is the material used in LED. Symbol of LED?
Light Emitting Diodes are made from exotic semiconductor compounds such as Gallium
Arsenide (GaAs), Gallium Phosphide (GaP), Gallium Arsenide Phosphide (GaAsP), Silicon
Carbide (SiC) or Gallium Indium Nitride (GaInN) all mixed together at different ratios to
produce a distinct wavelength of colour.

16. 58. If you are given 2 LEDs in series, then how will the resultant intensity of light be
affected?
First it will increase the resistance as it is connected in series, therefore the current will
decrease and intensity depends on current, thus less current so less intensity.
59. If you are given 2 LEDs in parallel, then how will the resultant intensity of light be
affected?
The intensity will remain same, as same voltage across each led is equal and resistance
also the same so same current flows.
60. What is an amplifier?
An amplifier is a device which produces a large electrical output of similar
Characteristics to that of the input parameters.
61. Define Transistor
Transistor consists of two junctions formed by sandwiching either P-type or N-type
semiconductor between a pair of opposite types.
62. When does a transistor act as a switch?
The transistor acts as a switch when it is operated at either cutoff region or saturation
region.

17. 63. What is biasing?
To use the transistor in any application it is necessary to provide sufficient voltage and
current to operate the transistor. This is called biasing.
64. What is operating point?
For the proper operation of the transistor a fixed level of current and voltages are
required. This values of currents and voltages defined at a point at which the transistor operate is
called operating point.
65. What are the types of Transistors?
They are of 4 types
1. BJT: Bi polar junction transistor again 2 types
NPN-BJT
PNP-BJT
2. FET: Field effect transistors again 2 types
P-Channel FET
N-Cannel FET
3. JFET: Junction field effect transistors they similar to FET.
4. MOSFET: Metal oxide semiconductor field effect transistor
These are of two types
a. Depletion MOSFET:
These are again classified into two types
N-Channel MOSFET
P-Channel MOSFET
b. Enhancement MOSFET:
These are again classified into two types
N-Channel MOSFET
P-Channel MOSFET

18. 66. What are the advantages of FET?
* Input impedance is very high. This allows high degree of Isolation between the input &
output Circuit.
*Current carriers are not crossing the junctions hence noise is highly reduced.
* It has a negative temperature Co-efficient of resistance. This avoids the thermal
runaway.
67. What are the advantages of MOSFET compared to JFET?
The input impedance of MOSFET is higher than that of JFET
68. What are the two modes of MOSFET?
(a) Depletion mode (b) Enhancement mode
69. Which is the most commonly used transistor configuration? Why?
The CE Configuration is most commonly used. The reasons are
* High Current gain
* High voltage gain
* High power
* Moderate input to output ratio.
70. What are the values of input resistance in CB, CE & CC Configuration
CB - Low about 75 CE - Medium About 750 CC - Very high about 750.
71. What are the differences between JFET & BJT?
S.NO JFET BJT
1. Unipolar device Bipolar device
2. High input impedance Low input impedance due to forward
bias
3. Voltage driven device Current driven device
4. Gain is characterized by transconductance
gain
Gain is characterized by
voltage
5. Low noise level High noise level
72. Define electronics symbol?

19. An electronic symbol is a pictogram used to represent
various electrical and electronic devices (such as wires, batteries, resistors, and transistors) in
a schematic diagram of an electrical or electronic circuit.
RESISTORS:
-fixed resistor -variable resistor
CAPACITORS:
-fixed capacitor -variable capacitor
INDUCTORS:
-Fixed inductor Variable inductor
TRANSFORMERS:
Primary secondary
SWITCHES:

20. SPST
SPDT
DPST
DPDT
SEMICONDUCTORS:
P-N Junction diode Zener diode
73. BREAD BOARD:
An experimental version of a circuit generally lay out on a flat board and assembled with
temporary connections so that circuit elements may be easily substituted or changed. The name
originates from the fact that early electrical circuits were actually wired on wood bread boards.
It is used to connect an electronic circuit temporarily for testing and experimentation.