148 + Interview Questions in Electronic Devices and Circuits in Electronics and Communication Engineering Page 2 InterviewSolution

51.	In a piezoelectric crystal, application of a mechanical stress would produce
Answer» Commonly material used as piezoelectric crystal is Barium Nitrate. Generally ferroelectric crystals and piezoelectric.

Discussion

52.	The value of in a transistor
Answer» a is about 0.98.

Discussion

53.	An one sided abrupt junction has 10/m of dopants on the lightly doped side, zero bias voltage and a built-in potential of 0.2 V. The depletion width of abrupt junction.( = 1.6 x 10 C, ε =16, ε = 8.87 x 10 F/) is
Answer» .

Discussion

54.	For BJT transistor. The maximum power dissipation is specified as 350 mW if ambient temperature is 25°C. If ambient temperature is 60°C the maximum power dissipation should be limited to about
Answer» 350 - 2.5 (60 - 25) ∼ 250 mW.

Discussion

55.	The concentration of minority carriers in a semiconductor depends mainly on
Answer» Minority carriers are generated due to thermal excitation.

Discussion

56.	Electrons can be emitted from a metal surface due to high electric field.
Answer» This is called field emission.

Discussion

57.	In an type semiconductor the fermi level is 0.35 eV below the conduction band, the concentration of donor atoms is increased to three times. The new position of Fermi level will be
Answer» Therefore, conductivity increases.

Discussion

58.	In a bipolar junction transistor the base region is made very thin so that
Answer» Since recombination in base region is minimum, I - IE.

Discussion

59.	Compared to bipolar junction transistor, a JFET has
Answer» JFET is voltage controlled device. Therefore its input impedance is high. But voltage gain is lower than in BJT.

Discussion

60.	SCR can be turned on by
Answer» If we apply the anode voltage above breakover voltage of SCR, SCR can be triggered. Also by sufficiently fast rate of rise of anode voltage and large gate current will trigger SCRon. During forward blocking most of the applied voltage appears across reverse biased junction J2. This voltage across J2 associated with leakage current may rise temperature of this junction. With increase in temperature, leakage current through junction J2 further increases and this cumulative process may turn on the SCR at some high temperature.

Discussion

61.	The breakdown voltage in a zener diode
Answer» Therefore, it is used in voltage regulator circuits.

Discussion

62.	A varactor diode is used for
Answer» Its voltage dependent capacitance is used for tuning.

Discussion

63.	One eV = 1.602 x 10 joules.
Answer» One electron has a charge 1.602 x 10-19 C, when it falls through 1 V, energy is 1 eV = 1.602 x 10-19 J.

Discussion

64.	If is plate current, is plate voltage and is grid voltage the - curve of a vacuum triode is = 0.003 ( + ). Typical values of and are
Answer» k has to be much higher than 1 so that grid is effective in controlling plate current n is not 1 because it is a nonlinear device.

Discussion

65.	The threshold voltage of an n-channel enhancement mode MOSFET is 0.5 when the device is biased at a gate voltage of 3V. Pinch off would occur at a drain voltage of
Answer» It is used with reverse bias.

Discussion

66.	The derating factor for a BJT transistor is about
Answer» For every 1°C rise in ambient temperature the power dissipation must be reduced by 2.5 mW so that transistor is safe.

Discussion

67.	The static characteristic of an adequately forward biased - junction is a straight line, if the plot is of __________ V → versus
Answer» Diode current equation I = Is(eV/Vr - 1) = eV/Vr - 1 = = eVs/VR = Vs = VR .

Discussion

68.	In an channel JFET
Answer» All currents are assumed positive when flowing into JFET.

Discussion

69.	An intrinsic silicon sample has 2 million free electrons. The number of holes in the sample is
Answer» In intrinsic semiconductor, the number of free electrons is equal to number of holes.

Discussion

70.	In an type semiconductor
Answer» Therefore, in n type semiconductor electrons are majority carriers.

Discussion

71.	Mobility of electrons and holes are equal.
Answer» Mobility of electrons is more than that of holes.

Discussion

72.	The intrinsic carrier concentration of silicon sample at 300 K is 1.5 x 10/m. If after doping, the number of majority carriers is 5 x 10/m. The minority carrier density is
Answer»

Discussion

73.	A diode is operating in forward region and the forward voltage and current are = 3 + 0.3 sin ω (volts) and = 5 + 0.2 sin ω (mA). The average power dissipated is
Answer» The contribution of sine terms to power dissipation is zero.

Discussion

74.	Two identical silicon diodes D and D are connected back to back shown in figure. The reverse saturation current of each diode is 10 amps and the breakdown voltage V is 50 . Evaluate the voltages V and V dropped across the diodes D and D assuming KT/ to be 25 m V.
Answer» According to figure, D2 is forward bias, D1 is reverse biased. Reverse saturation current I0 = 10-8A. in clockwise direction. For Diode D2 Is = I0 Here Is = I0 eqv2/kT = 2 or ev2/0.026 = 2 V2 = 0.018 V Drop across D1 = V1 = 5 - 0.018 4.98 V By KVL in mesh, VD1 = -4.98 V, VD2 = 0.018 V.

Discussion

75.	The mean free path of conduction electrons in copper is about 4 x 10 m. For a copper block, find the electric field which can give, on an average, 1 eV energy to a conduction electron
Answer» Work (Energy) = F x d 1 eV = e.E x d 2.5 x 107 V/m.

Discussion

76.	When a -- transistor is properly biased to operate in active region the holes from emitter.
Answer» The reason that collector current is nearly equal to emitter current.

Discussion

77.	A Varactor diode has
Answer» The applied bias governs the width of depletion layer. Therefore, capacitance varies with bias.

Discussion

78.	The most important set of specifications of transformer oil includes
Answer» Oil used in transformer work as cooling as well as dielectric strength.

Discussion

79.	At room temperature a semiconductor material is
Answer» At 0 K a semiconductor is perfect insulator. At room temperature it is slightly conducting.

Discussion

80.	A voltage of 9 V is applied in forward direction to a semiconductor diode in series with a load resistance of 1000 &ohm;. The voltage across the load resistance is zero. It indicates that
Answer» Since there is no voltage across load resistor, the current is zero and diode is open-circuit. If diode is short- circuited or resistor is open-circuited almost 9 V will appear across resistor.

Discussion

81.	If the drift velocity of holes under a field gradient of 100 V/m in 5 m/s, their mobility (in SI units) is
Answer» .

Discussion

82.	When a diode is not conducting, its bias is
Answer» Diode conducts only when forward biased. There is no conduction when bias is zero or reverse.

Discussion

83.	The SCR would be turned OFF by voltage reversal of applied anode-cathode ac supply of frequency of
Answer» For inverter grade SCR, typical turn off time (toff) is 5 to 50 μsec while 50 to 100 μsec for converter grade SCR. Hence supply frequency of 5 kHz will turn off the SCR by voltage reversal because = 200 μsec.

Discussion

84.	The number of valence electrons in a donor atom is
Answer» Therefore, it can donate one electron.

Discussion

85.	An electron rises through a voltage of 100 V. The energy acquired by it will be
Answer» When an electron rises through 1 V, energy = 1 eV.

Discussion

86.	The amount of photoelectric emission current depends on the frequency of incident light.
Answer» It depends on intensity of incident light.

Discussion

87.	When a - junction is forward biased
Answer» Forward voltage decreases the width of depletion layer leading to low resistance.

Discussion

88.	The carriers of channel JFET are
Answer» In n type semiconductors carriers are electrons.

Discussion

89.	The depletion layer around - junction in JFET consists of
Answer» Depletion layer always has immobile charges.

Discussion

90.	Junction temperature is always the same as room temperature.
Answer» When the device is being used, junction temperature is higher than room temperature.

Discussion

91.	If the reverse voltage across a - junction is increased three times, the junction capacitance
Answer» Increase of reverse voltage widens the depletion layer and junction capacitance decreases. However the decrease in capacitance is not proportional to increase in voltage.

Discussion

92.	Which of these has highly doped and region?
Answer» Tunnel diode has heavily doped p and n regions leading to very thin depletion layer.

Discussion

93.	Measurement of Hall coefficient enables the determination of
Answer» If a potential difference is developed across a current carrying metal strip when the strip is placed in transverse magnetic field. Hall effect is very weak in metals, but it is large semiconductors.

Discussion

94.	The units for transconductance are
Answer» Its units are the same as the units of conductance.

Discussion

95.	In which material do conduction and valence bands overlap
Answer» This is the reason for high conductivity of conductors.

Discussion

96.	For a photoconductor with equal electron and hole mobilities and perfect ohmic contacts at the ends, an increase in illumination results in
Answer» Increase in illumination reduces resistance of a photoconductor.

Discussion

97.	Discrete transistors T and T having maximum collector current rating of 0.75 amp are connected in parallel as shown in the figure, this combination is treated as a single transistor to carry a total current of 1 ampere, when biased with self bias circuit. When the circuit is switched on, T draws 0.55 amps and T draws 0.45 amps. If the supply is kept on continuously, ultimately it is very likely that
Answer» T1 draws 0.55 A and T2 draws 0.45 A, T1 will get more heated and correct increase. Ultimately, I1 = 1A and I2 = 0.

Discussion

98.	The number of - junctions in a semiconductor diode are
Answer» Semiconductor diode has one p-n junction, BJT has two and SCR has three p-n junctions.

Discussion

99.	Which of these has degenerate and materials?
Answer» Tunnel diode has heavily doped p and n layers called degenerate p and n materials.

Discussion

100.	A Schottky diode clamp is used along with switching BJT for
Answer» Schottky diode has very low switching time.

Discussion

Explore topic-wise InterviewSolutions in .

In a piezoelectric crystal, application of a mechanical stress would produce

The value of in a transistor

An one sided abrupt junction has 10/m of dopants on the lightly doped side, zero bias voltage and a built-in potential of 0.2 V. The depletion width of abrupt junction.( = 1.6 x 10 C, ε =16, ε = 8.87 x 10 F/) is

For BJT transistor. The maximum power dissipation is specified as 350 mW if ambient temperature is 25°C. If ambient temperature is 60°C the maximum power dissipation should be limited to about

The concentration of minority carriers in a semiconductor depends mainly on

Electrons can be emitted from a metal surface due to high electric field.

In an type semiconductor the fermi level is 0.35 eV below the conduction band, the concentration of donor atoms is increased to three times. The new position of Fermi level will be

In a bipolar junction transistor the base region is made very thin so that

Compared to bipolar junction transistor, a JFET has

SCR can be turned on by

The breakdown voltage in a zener diode

A varactor diode is used for

One eV = 1.602 x 10 joules.

If is plate current, is plate voltage and is grid voltage the - curve of a vacuum triode is = 0.003 ( + ). Typical values of and are

The threshold voltage of an n-channel enhancement mode MOSFET is 0.5 when the device is biased at a gate voltage of 3V. Pinch off would occur at a drain voltage of

The derating factor for a BJT transistor is about

The static characteristic of an adequately forward biased - junction is a straight line, if the plot is of __________ V → versus

In an channel JFET

An intrinsic silicon sample has 2 million free electrons. The number of holes in the sample is

In an type semiconductor

Mobility of electrons and holes are equal.

The intrinsic carrier concentration of silicon sample at 300 K is 1.5 x 10/m. If after doping, the number of majority carriers is 5 x 10/m. The minority carrier density is

A diode is operating in forward region and the forward voltage and current are = 3 + 0.3 sin ω (volts) and = 5 + 0.2 sin ω (mA). The average power dissipated is

Two identical silicon diodes D and D are connected back to back shown in figure. The reverse saturation current of each diode is 10 amps and the breakdown voltage V is 50 . Evaluate the voltages V and V dropped across the diodes D and D assuming KT/ to be 25 m V.

The mean free path of conduction electrons in copper is about 4 x 10 m. For a copper block, find the electric field which can give, on an average, 1 eV energy to a conduction electron

When a -- transistor is properly biased to operate in active region the holes from emitter.

A Varactor diode has

The most important set of specifications of transformer oil includes

At room temperature a semiconductor material is

A voltage of 9 V is applied in forward direction to a semiconductor diode in series with a load resistance of 1000 &ohm;. The voltage across the load resistance is zero. It indicates that

If the drift velocity of holes under a field gradient of 100 V/m in 5 m/s, their mobility (in SI units) is

When a diode is not conducting, its bias is

The SCR would be turned OFF by voltage reversal of applied anode-cathode ac supply of frequency of

The number of valence electrons in a donor atom is

An electron rises through a voltage of 100 V. The energy acquired by it will be

The amount of photoelectric emission current depends on the frequency of incident light.

When a - junction is forward biased

The carriers of channel JFET are

The depletion layer around - junction in JFET consists of

Junction temperature is always the same as room temperature.

If the reverse voltage across a - junction is increased three times, the junction capacitance

Which of these has highly doped and region?

Measurement of Hall coefficient enables the determination of

The units for transconductance are

In which material do conduction and valence bands overlap

For a photoconductor with equal electron and hole mobilities and perfect ohmic contacts at the ends, an increase in illumination results in

The number of - junctions in a semiconductor diode are

Which of these has degenerate and materials?

A Schottky diode clamp is used along with switching BJT for