EDC Lab Viva Questions with Answers
Electronic Devices and Circuits Lab Viva Questions with Answers
1.
Differentiate Electronics and Electrical Engg.?
We can say that electronics is the branch of
science which deals with vacuum tubes, semi conductor materials like diodes,
transistor etc. The maximum allowed voltage range of electronics engg is about
0 to 30 V. Electrical is the branch of science which deals with the currents in
conductors, in other words, we can say that electrical engg deals with 0 to 230
V, 50 Hz operating devices. Operation of devices like motors, generators etc
are included in electrical engg.
2.
Classify materials in terms of conductivity?
By the property of conduction of electricity,
materials can be mainly classified as conductors, semiconductors and
insulators. In conductors, the valance band (VB) and conduction band (CB)
overlaps each other (i.e., energy gap is zero), so the electrons can easily
move from valance band to the conduction band. Examples are Gold, Copper,
Silver etc. In insulators, the energy gap is very wide (about 3 to 5 eV) and
hence the electrons cannot flow from VB to CB. In semiconductors, the energy
gap is narrower so the electrons from VB can move to CB by absorbing energy.
The energy gap of Si is 1.1 eV and for Ge it is 0.7 eV.
3.
Differentiate Semiconductor and conductors?
Semiconductor has four electrons in its VB.
The energy gap of semiconductors is about 1 eV. So at normal condition the
electrons cannot move from VB to CB. By giving some external energy to the
electrons, electrons can move from VB to CB. The best semiconductors are Si,
Ge, etc. The conductors have more than four electrons in its VB. The energy gap
of conductors is 0 eV. So the electrons can easily move from VB to CB. Best
conductors are Ag, Al, Cu.
4.
Compare intrinsic and extrinsic Semiconductors?
Intrinsic semiconductors are the pure form of
semiconductors. At room temperature, the conductivity of intrinsic
semiconductor is zero. At room temperature, its VB is totally filled and the CB
is empty. When some heat energy is supplied (as temperature increases),
electrons can jump to CB and can move randomly. As temperature increases, the
conductivity increases and the resistivity decreases. Extrinsic semiconductors
are formed by intentionally adding impurities on it. At room temperature, the
extrinsic semiconductor is very little conductive. The impurities added can be
trivalent (resulting P type materials) or pentavalent (resulting N type
materials).
5.
Explain different types of extrinsic semiconductors and discuss their formation?
The extrinsic semiconductors are made of by
adding impurities on fourth group elements of periodic table (Si, Ge etc).
There are mainly two types of extrinsic semiconductors- P Type and N Type. P
types are formed by adding trivalent impurities (third group elements in
Periodic table such as arsenic, antimony, phosphorus) to the fourth group
elements. N type semiconductors are formed by adding pentavalent impurities
(fifth group elements like aluminum, boron etc) to the fourth group elements.
6.
Discuss the process of doping?
Simply we
can say that doping is the process of adding impurities. Extrinsic
semiconductors are made by doping process. The two types of doped semiconductor
materials are P type and N type materials.
7.
Discuss the process of formation of PN Junction?
A P-N junction (technically termed as diode)
is a piece of semiconductor material in which it’s one half is doped by P type
impurity and the other half is doped by N type impurity. P-N junction was
developed in the year 1936. The main advantage of P-N junction is it passes
current in only one direction. So we can say that PN junction act as a switch
in electronic circuits. The main application of PN junction is rectifier
circuits.
8.
Explain about cut in voltage (Barrier Potential)?
The cut in voltage is the minimum voltage in
which a PN junction starts its conduction. For Silicon diode, it is 0.7 Volts
and for Ge diode is 0.3 V. That is when the external applied voltage crosses
the barrier potential, the diode conducts electrons.
9.
Discuss about Forward bias and Reverse bias conditions?
If the externally applied voltage of the anode
(P) is greater than the cathode (N) voltage in a PN junction diode, the diode
is said to be in forward biased condition. If the anode voltage is less than
the cathode voltage, then the diode is in reverse biased condition.
10.
Compare between Diffusion and Drift currents?
The current formed by the diffusion of holes
or electrons is termed as the diffusion current. In other words we can say that
due to the non uniform concentration of charged particles, the transportation
of charge occurs and this current is termed as diffusion current. Diffusion
current doesn’t need an external applied electric field. Drift current is the
current occurred due to the effect of an externally applied electric field.
That is the motion of charged particles due to the effect of an externally
applied electric field. If there is no electric field, the drift current
becomes zero.
11.
Describe the meaning of 1N4007?
IN4007 is
actually represents a diode. The expansion of the diode is
IN means
it is a single junction diode
400x indicates
the voltage, current and power
4007 represents
the reverse voltage from 50V to 1000V, the maximum forward current is 1A
12. Justify the Diode current Equation?
The diode equation can be derived as
I=Io(e(V/ηVT)-1),
Where, Io is the Reverse saturation current,
and the value of η=1 for germanium,
and 2 for silicon.
13.
What you mean by Peak inverse voltage (PIV)?
PIV is
the maximum affordable reverse voltage of a diode. When the applied reverse
voltage exceeds the PIV, the PN junction gets damaged (diode goes to breakdown
condition). It is also known as Peak Reverse Voltage (PRV). The PIV is also
termed as reverse breakdown voltage.
14
Discuss about Reverse saturation current?
The reverse saturation current (Ico) is
produced due to the diffusive flow of minority charge carriers, when a diode is
at reverse biased condition. At R-B condition, the holes will get attracted to
the negative terminal of the applied cell and the electrons will get attracted
to the positive terminal of the cell. Hence the depletion width increases and
the flow of charges through the junction becomes zero. But there exists
thermally produced some electron-hole pairs. These thermally generated
electron-hole pairs are less in number and the electrons produced are repelled
by the –ve terminal and the holes are repelled by the +ve terminal. This will
cause a small current passes through the PN junction. This current is very
small and is almost constant.
15.
Discuss about the testing of diode by a multimeter?
The working condition of diode can be easily
tested by a multimeter. For testing a diode, the anode (P side) of the diode is
connected to the positive terminal of multimeter and the cathode (N side) of
the diode is connected to the negative terminal of the multimeter. If the
readed voltage is in the range of 0.3 to 0.7 Volts, then the diode is in good
condition.
16.
Mention the capacitive effects formed in a P-N junction.
There are mainly two types of capacitance
formed in a PN junction.
a. Diffusion Capacitance: The diffusion
capacitance occurs in forward biased condition.
b. Transition capacitance: Transition
capacitance occurs in the reverse biased condition.
17.Discuss
about the Break down condition, compare avalanche Break down and Zener Break down?
The breakdown occurs due to the impact of
ionization of electron-hole pair in a PN junction diode is termed as the
Avalanche breakdown.
At the reverse biased voltage condition, the
electron hole pair breaks in a zener diode and this breakdown is termed as
zener breakdown.
18.
Discuss the effect of temperature on reverse saturation current and barrier
voltage?
As the temperature increases, the reverse
saturation current also increases. As the temperature raise by 10 degrees, the
reverse saturation current doubles.
As the temperature increases, the barrier
voltage decreases. For every temperature increase of 1 degree, the barrier
voltage decreases by 2.5 mv
19.
Differentiate between static and dynamic resistances?
The ratio of voltage and current (V-I ratio)
at the Q-point(operating point) is the static resistance.
The inverse to the slop of the forward bias
characteristic curve at operating (Q point) is termed as the dynamic
resistance.
20.
Mention the applications of PN Diode and
Zener diode?
The main
applications of a PN junction diode are: Rectifier, clipper, clamper, switch etc.
Voltage
regulator circuit is the main application of zener diode.
21.What
is the major difference of PN junction and zener diode?
The main
difference of PN junction diode and zener diode is the PN junction is lightly
dopped and the zener diode is heavily dopped.
22.
Zener diode is not used in forward biased condition. justify your answer?
The response of a zener diode in forward bias
condition is same as that of a PN junction diode. So generally the zener diode
is used in reverse bias state with zener breakdown.
23.Discuss
the effect of temperature on Zener diode?
The effect
of temperature on zener diode depends on the breakdown voltage. If the
breakdown voltage (Vz) is less than 6V (breakdown voltage), Vz
is inversely proportional to temperature.
The
breakdown voltage Vz is directly proportional to temperature, if the
the breakdown voltage is greater than 6V
24.
Give the advantage of silicon over germanium?
The breakdown
voltage of silicon is more than germanium. The reverse saturation current of
silicon is less than that of germanium. Since the raw material is sand, silicon
diode is cheaper than germanium diode. The cut-off voltage of silicon diode is
0.7 V and that of germanium is 0.3V.
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