Indiabix Electronic Devices and Circuits

The most commonly used semiconductor material is

a silicon

b germanium

c mixture of silicon and germanium

d none of the above

a silicon

In which of these is reverse recovery time nearly zero?

a Zener diode

b Tunnel diode

c Schottky diode

d PIN diode

c Schottky diode

A transistor has a current gain of 0.99 in the CB mode. Its current gain in the CC mode is

a 100

b 99

c 1.01

d 0.99

a 100

1 + B; B = a/(1-a)

In an n channel JFET, the gate is

a n type

b p type

c either n or p

d partially n & partially p

b p type

At very high temperatures the extrinsic semi conductors become intrinsic because

a drive in diffusion of dopants and carriers

b band to band transition dominants over impurity ionization

c impurity ionization dominants over band to band transition

d band to band transition is balanced by impurity ionization

b band to band transition dominants over impurity ionization

In a p type material the Fermi level is 0.3 eV above valence band. The concentration of acceptor atoms is increased. The new position of Fermi level is likely to be

a 0.5 eV above valence band

b 0.28 eV above valence band

c 0.1 eV above valence band

d below the valence band

b 0.28 eV above valence band

An LED has a rating of 2 V and 10 mA. It is used along with 6V battery. The range of series resistance is

a 0 to 200 Ω

b 200 - 400 Ω

c 200 Ω and above

d 400 Ω and above

d 400 Ω and above

A silicon (PN) junction at a temperature of 20°C has a reverse saturation current of 10 pico Ampere. The reverse saturation current at 40°C for the same bias is approximately.

a 30 pA

b 40 pA

c 50 pA

d 60 pA

b 40 pA

for every 10C, I doubles

An amplifier without feedback has a voltage gain of 50, input resistance of 1 kΩ and output resistance of 2.5 kΩ. The input resistance of the current shunt -ve feedback amplifier using the above amplifier with a feedback factor of 0.2 is

a 1/11 kΩ

b 1/5 kΩ

c 5 kW

d 11 kW

a 1/11 kΩ

Ri/(1+AB)

As compared to an ordinary semiconductor diode, a Schottky diode

a has lower cut in voltage

b has higher cut in voltage

c lower reverse saturation current

d both (b) and (c)

a has lower cut in voltage

As compared to an ordinary semiconductor diode, a Schottky diode

a has higher reverse saturation current

b has higher reverse saturation current and higher cut in voltage

c has higher reverse saturation current and lower cut in voltage

d has lower reverse saturation current and lower cut in voltage

c has higher reverse saturation current and lower cut in voltage

Crossover distortion behaviour is characteristic of

a class A O/P stage

b class B O/P stage

c class AB output stage

d common pulse O/P state

b class B O/P stage

If alpha-ac for transistor is 0.98 then βac is equal to

a 51

b 49

c 47

d 45

b 49

In an n-p-n transistor biased for operation in forward active region

a emitter is positive with respect to base

b collector is positive with respect to base

c base is positive with respect to emitter and collector is positive with respect to base

d none of the above

c base is positive with respect to emitter and collector is positive with respect to base

A zener diode is used in

a voltage regulator circuit

b amplifier circuits

c both voltage regulator and amplifier circuit

d none of the above

a voltage regulator circuit

In a zener diode

a the forward current is very high

b sharp breakdown occurs at a certain reverse voltage

c the ratio v-i can be negative

d there are two p-n junctions

b sharp breakdown occurs at a certain reverse voltage

In a bipolar transistor which current is largest

a collector current

b base current

c emitter current

d base current or emitter current

c emitter current

In a degenerate n type semiconductor material, the Fermi level,

a is in valence band

b is in conduction band

c is at the centre in between valence and conduction bands

d is very near valence band

b is in conduction band

A potential of 7 V is applied to a silicon diode. A resistance of 1 K ohm is also in series with the diode. The current is

a 7 mA

b 6.3 mA

c 0.7 mA

d 0

b 6.3 mA

Calculate the stability factor and change in IC from 25°C to 100°C for, β = 50, RB/ RE = 250, ΔIC0 = 19.9 nA for emitter bias configuration.

a 42.53, 0.85 μA

b 40.91, 0.58 μA

c 40.91, 0.58 μA

d 41.10, 0.39 μA

a 42.53, 0.85 μA

ΔIC = S*ΔIC0

A periodic voltage has following value for equal time intervals changing suddenly from one value to next... 0, 5, 10, 20, 50, 60, 50, 20, 10, 5, 0, -5, -10 etc. Then rms value of the waveform is

a 31 V

b 32 V

c insufficient data

d none of these

a 31 V

The word enhancement mode is associated with

a tunnel diode

b MOSFET

c JFET

d photo diode

b MOSFET

In which region of a CE bipolar transistor is collector current almost constant?

a Saturation region

b Active region

c Breakdown region

d Both saturation and active region

b Active region

The power dissipation in a transistor is the product of

a emitter current and emitter to base voltage

b emitter current and collector to emitter voltage

c collector current and collector to emitter voltage

d none of the above

c collector current and collector to emitter voltage

The normal operation of JFET is

a constant voltage region

b constant current region

c both constant voltage and constant current regions

d either constant voltage or constant current region

b constant current region

An incremental model of a solid state device is one which represents the

a ac property of the device at desired operating point

b dc property of the device at all operating points

c complete ac and dc behaviour at all operating points

d ac property of the device at all operating points

a ac property of the device at desired operating point

Which of the following is used for generating time varying wave forms?

a MOSFET

b PIN diode

c Tunnel diode

d UJT

d UJT

n-type semiconductors

a are negatively charged

b are produced when indium is added as impurity to germanium

c are produced when phosphorus is added as impurity to silicon

d none of the above

c are produced when phosphorus is added as impurity to silicon

n type semiconductor is produced when pentavalent impurity is added.

The voltage across a zener diode

a is constant in forward direction

b is constant in reverse direction

c is constant in both forward and reverse directions

d none of the above

b is constant in reverse direction

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

a 1.5 V

b 2.5 V

c 3.5 V

d 4.5 V

b 2.5 V

Vp = Vgs-Vth

Which of these has degenerate p and n materials?

a Zener diode

b PIN diode

c Tunnel diode

d Photo diode

c Tunnel diode

A Schottky diode clamp is used along with switching BJT for

a reducing the power dissipation

b reducing the switching time

c increasing the value of β

d reducing the base current

b reducing the switching time

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

a plastic deformation of the crystal

b magnetic dipoles in the crystal

c electrical polarization in the crystal

d shift in the Fermi level

c electrical polarization in the crystal

In which of the following is the width of junction barrier very small?

a Tunnel diode

b Photo diode

c PIN diode

d Schottky diode

d Schottky diode

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

a will decrease

b will increase

c will decrease by an approximate factor of about 2

d will increase by an approximate factor of about 2

c will decrease by an approximate factor of about 2

Which of these has highly doped p and n region?

a PIN diode

b Tunnel diode

c Schottky diode

d Photodiode

b Tunnel diode

The depletion layer around p-n junction in JFET consists of

a hole

b electron

c immobile charges

d none of the above

c immobile charges

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

a diffuse through base into collector region

b recombine with electrons in base

c recombine with electrons in emitter

d none of the above

a diffuse through base into collector region

Assertion (A): Silicon is preferred over germanium in manufacture of semiconductor devices.

Reason (R): Forbidden gap in silicon is more than that in germanium.

a Both A and R are true and R is correct explanation of A

b Both A and R are true but R is not a correct explanation of A

c A is true but R is false

d A is false but R is true

a Both A and R are true and R is correct explanation of A

At room temperature a semiconductor material is

a perfect insulator

b conductor

c slightly conducting

d any of the above

c slightly conducting

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

a log I Vs log V

b log I Vs V

c I Vs log V

d I Vs V

b log I Vs V

In an n channel JFET

a ID, IS and IG are considered positive when flowing into the transistor

b ID and IS are considered positive when flowing into transistor and IG is considered positive when flowing out of it

c ID, IS, IG are considered positive when flowing out of transistor

d IS and IG are considered positive when flowing into transistor and ID is considered positive when flowing out of it

a ID, IS and IG are considered positive when flowing into the transistor

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

a 15 mW

b about 15 mW

c 1.5 mW

d about 1.5 mW

b about 15 mW

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

a 100 mW

b 250 mW

c 450 mW

d 600 mW

b 250 mW

350-2.5(deltaT)

The concentration of minority carriers in a semiconductor depends mainly on

a the extent of doping

b temperature

c the applied bias

d none of the above

b temperature

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

a recombination in base region is minimum

b electric field gradient in base is high

c base can be easily fabricated

d base can be easily biased

a recombination in base region is minimum

Compared to bipolar junction transistor, a JFET has

a lower input impedance

b high input impedance and high voltage gain

c higher voltage gain

d high input impedance and low voltage gain

d high input impedance and low voltage gain

The drain characteristics of JFET in operating region, are

a inclined upwards

b almost flat

c inclined downwards

d inclined upwards or downwards

b almost flat

As temperature increases

a the forbidden energy gap in silicon and germanium increase

b the forbidden energy gap in silicon and germanium decrease

c the forbidden energy gap in silicon decreases while that in germanium decreases

d the forbidden energy gap in silicon increases while that in germanium decreases

b the forbidden energy gap in silicon and germanium decrease

Which of the following devices has a silicon dioxide layer?

a NPN transistor

b Tunnel diode

c JFET

d MOSFET

d MOSFET

For an P-channel enhancement type MOSFET determine the drain current if K = 0.278 x 10-3A/V2, VGS = -4V, VT = -2V, Voltage equivalent at 27°C = 26 mV.

a 10 mA

b 1.11 mA

c 0.751 mA

d 46.98 mA

b 1.11 mA

MOSFET Id = k(|Vgs|-|Vt|)^2

Which of the following elements act as donor impurities?

1 Gold

2 Phosphorus

3 Boron

4 Antimony

5 Arsenic

6 Indium

Select the answer using the following codes :

a 1, 2 and 3

b 1, 2, 4, and 6

c 3, 4, 5 and 6

d 2, 4 and 5

d 2, 4 and 5

2 Phosphorus

4 Antimony

5 Arsenic

The breakdown voltage in a zener diode

a is almost constant

b is very small

c may destroy the diode

d decreases with increase in current

a is almost constant

A varactor diode is used for

a tuning

b rectification

c amplification

d rectification and amplification

a tuning

Assertion (A): When VDS is more than rated value the drain current in a JFET is very high.

Reason (R): When VDS is more than rated value, avalanche breakdown occurs.

a Both A and R are true and R is correct explanation of A

b Both A and R are true but R is not a correct explanation of A

c A is true but R is false

d A is false but R is true

a Both A and R are true and R is correct explanation of A

Assertion (A): A high junction temperature may destroy a diode.

Reason (R): As temperature increases the reverse saturation current increases.

a Both A and R are true and R is correct explanation of A

b Both A and R are true but R is not a correct explanation of A

c A is true but R is false

d A is false but R is true

a Both A and R are true and R is correct explanation of A

When a diode is not conducting, its bias is

a forward

b zero

c reverse

d zero or reverse

d zero or reverse

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

a 30 kHz

b 15 kHz

c 5 kHz

d 20 kHz

c 5 kHz

The number of valence electrons in a donor atom is

a 2

b 3

c 4

d 5

d 5

A Varactor diode has

a a fixed capacitance

b a fixed inductance

c a voltage variable capacitance

d a current variable inductance

c a voltage variable capacitance

The most important set of specifications of transformer oil includes

a dielectric strength and viscosity

b dielectric strength and flash point

c flash point and viscosity

d dielectric strength, flash point and viscosity

d dielectric strength, flash point and viscosity

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

a diode is short circuited

b diode is open circuited

c resistor is open circuited

d diode is either o.c or s.c

b diode is open circuited

The derating factor for a BJT transistor is about

a 0.5 mW/°C

b 2.5 mW/°C

c 10 mW/°C

d 25 mW/°C

b 2.5 mW/°C

Assertion (A): When reverse voltage across a p-n junction is increased, the junction capacitance decreases.

Reason (R): Capacitance of any layer is inversely proportional to thickness.

a Both A and R are true and R is correct explanation of A

b Both A and R are true but R is not a correct explanation of A

c A is true but R is false

d A is false but R is true

a Both A and R are true and R is correct explanation of A

In an n 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

a 0.35 eV below conduction band

b about 0.32 eV below conduction band

c about 0.32 eV above conduction band

d about 0.1 eV below conduction band

b about 0.32 eV below conduction band

Assertion (A): In a BJT, the base region is very thick.

Reason (R): In p-n-p transistor most of holes given off by emitter diffuse through the base.

a Both A and R are true and R is correct explanation of A

b Both A and R are true but R is not a correct explanation of A

c A is true but R is false

d A is false but R is true

d A is false but R is true

Assertion (A): The behaviour of FET is similar to that of a pentode.

Reason (R): FETs and vacuum triode are voltage controlled devices.

a Both A and R are true and R is correct explanation of A

b Both A and R are true but R is not a correct explanation of A

c A is true but R is false

d A is false but R is true

a Both A and R are true and R is correct explanation of A

CR can be turned on by

1 applying anode voltage at a sufficient fast rate

2 applying sufficiently large anode voltage

3 increasing the temperature of SCR to a sufficiently

4 applying sufficiently large gate current.

In a bipolar transistor

a recombination in base regions of both n-p-n and p-n-p transistor is low

b recombination in base regions of both n-p-n and p-n-p transistors is high

c recombination in base region of n-p-n transistor is low but that in p-n-p transistor is high

d recombination in base region of p-n-p transistor is low but that in n-p-n transistor is high

a recombination in base regions of both n-p-n and p-n-p transistor is low

If for a silicon n-p-n transistor, the base to emitter voltage (VBE) is 0.7 V and the collector to base voltage VCB is 0.2 Volt, then the transistor is operating in the

a normal active mode

b saturation mode

c inverse active mode

d cut off mode

a normal active mode

Transistor will operate in active mode because

VBE = 0.7 volt, (Base emitter junction is forward biased)

VCB = - VBC = - 0.2 V (Base to collector junction is reverse biased).

GaAs has an energy gap 1.43 eV the optical cut off wavelength of GaAs would lie in the

a visible region of the spectrum

b infrared region of the spectrum

c ultraviolet region of the spectrum

d for ultraviolet region of the spectrum

b infrared region of the spectrum

Which of the following is basically a voltage controlled capacitance?

a Zener diode

b Diode

c Varactor diode

d LED

c Varactor diode

The threshold voltage of a MOSFET can be lowered by

1 using thin gate oxide

2 reducing the substrate concentration

3 increasing the substrate concentration.

Of the above statement

a 3 alone is correct

b 1 and 2 are correct

c 1 and 3 are correct

d 2 alone is correc

c 1 and 3 are correct

1 using thin gate oxide

3 increasing the substrate concentration.

An increase in junction temperature of a semiconductor diode

a causes a small increase in reverse saturation current

b causes a large increase in reverse saturation current

c does not affect reverse saturation current

d may cause an increase or decrease in reverse saturation current depending on rating of diode

b causes a large increase in reverse saturation current

An air gap provided in the iron core of an inductor prevents

a flux leakage

b hysteresis loss

c core saturation

d heat generation

c core saturation

Generally, the gain of a transistor amplifier falls at high frequency due to the

a internal capacitance of the device

b coupling capacitor at the I/P

c skin effect

d coupling capacitor at the O/P

a internal capacitance of the device

Which of these has a layer of intrinsic semiconductor?

a Zener diode

b PIN diode

c Photo diode

d Schottky diode

b PIN diode

Assertion (A): When Diode used as rectifier the reverse breakdown voltage should not be exceeded.

Reason (R): A high inverse voltage can destroy a p-n junction.

a Both A and R are true and R is correct explanation of A

b Both A and R are true but R is not a correct explanation of A

c A is true but R is false

d A is false but R is true

a Both A and R are true and R is correct explanation of A

Assertion (A): In design of circuit using BJT, a derating factor is used.

Reason (R): As the ambient temperature increases, heat dissipation becomes slower.

a Both A and R are true and R is correct explanation of A

b Both A and R are true but R is not a correct explanation of A

c A is true but R is false

d A is false but R is true

a Both A and R are true and R is correct explanation of A

What is the effect of cut in voltage on the wave form of output as compared to input in a semiconductor diode?

a The duration of output waveform is less than 180°

b Output voltage is less than input voltage

c Output voltage is more than input voltage

d Both (a) and (b)

d Both (a) and (b)

a The duration of output waveform is less than 180°

b Output voltage is less than input voltage

Assertion (A): A JFET behaves as a resistor when VGS < VP.

Reason (R): When VGS < VP, the drain current in a JFET is almost constant.

a Both A and R are true and R is correct explanation of A

b Both A and R are true but R is not a correct explanation of A

c A is true but R is false

d A is false but R is true

c A is true but R is false

In a reverse biased P-N junction, the current through the junction increases abruptly at

a zero voltage

b 1.2 V

c 0.72 V

d breakdown voltage

d breakdown voltage

The channel of JFET consists of

a p type material only

b n type material only

c conducting material

d either p or n type material

d either p or n type material

In a bipolar junction transistor adc = 0.98, ICO= 2 μA and 1B = 15 μA. The collector current IC is

a 635 mA

b 735 mA

c 835 mA

d 935 mA

b 735 mA

The voltage across the secondary of the transformer in a half wave rectifier with a shunt capacitor filter is 50 volts. The maximum voltage that will occur on the reverse biased diode will be

a 100 V

b 88 V

c 50 V

d 25 V

a 100 V

Assertion (A): The forward resistance of a p-n diode is not constant.

Reason (R): The v-i characteristics of p-n diode is non-linear.

a Both A and R are true and R is correct explanation of A

b Both A and R are true but R is not a correct explanation of A

c A is true but R is false

d A is false but R is true

a Both A and R are true and R is correct explanation of A

In given figure a silicon diode is carrying a constant current of 1 mA. When the temperature of the diode is 20°C, VD is found to be 700 mV. If the temperature rises to 40°C, VD becomes approximately equal to

a 747 mV

b 660 mV

c 680 mV

d 700 mV

a 747 mV

V1/V2 = T1/T2

N-type silicon is obtained by doping silicon with

a germanium

b aluminium

c boron

d phosphorus

d phosphorus

When a p-n junction is reverse biased

a holes and electrons move away from the junction

b holes and electrons move towards the junction

c holes move towards junction and electrons move away from junction

d holes move away from junction and electrons move towards junction

a holes and electrons move away from the junction

If a sample of germanium and a sample of Si have the impurity density and are kept at room temperature then

a both will have equal value of resistivity

b both will have equal -ve resistivity

c resistivity of germanium will be higher than that of silicon

d resistivity of Si will be higher than of germanium

d resistivity of Si will be higher than of germanium

Assertion (A): In a BJT base current is very small.

Reason (R): In a BJT recombination in base region is high.

a Both A and R are true and R is correct explanation of A

b Both A and R are true but R is not a correct explanation of A

c A is true but R is false

d A is false but R is true

c A is true but R is false

A reverse voltage of 18 V is applied to a semiconductor diode. The voltage across the depletion layer is

a 0 V

b 0.7 V

c about 10 V

d 18 V

d 18 V

In degenerate p type semiconductor material, the Fermi level,

a is in the valence band

b is in conduction band

c is at the centre in between valence and conduction bands

d is very near conduction band

a is in the valence band

Which of the following devices has substrate?

a JFET

b Depletion Type MOSFET

c Enhancement type MOSFET

d Both (b) and (c)

d Both (b) and (c)

As comparated to an ordinary p-n diode, the extent of impurity atoms in a tunnel diode

a is more

b is less

c may be more or less

d is almost the same

a is more

In active filter circuits, inductances are avoided mainly because they

a are always associated with some resistance

b are bulky and unsuitable for miniaturisation

c are non-linear in nature

d saturate quickly

b are bulky and unsuitable for miniaturisation

When a p-n-p transistor is operating in active region, the current in the n region is due to

a only holes

b only electrons

c mainly holes

d mainly electrons

c mainly holes

In a JFET

a drain current is very nearly equal to source current

b drain current is much less than source current

c drain current may be equal to or less than source current

d drain current may be even more than source current

a drain current is very nearly equal to source current

In a reverse biased p-n junction, the reverse bias is 4V. The junction capacitance is about

a 0.1 F

b 4 μF

c 10 nF

d 20 pF

d 20 pF

A JFET operates in ohmic region when

a VGS = 0

b VGS is less than pinch off voltage

c VGS = is Positive

d VGS = VDS

b VGS is less than pinch off voltage