WBCHSE Class 12 Physics Semiconductor Electronics Multiple Choice Questions

WBCHSE Class 12 Physics Semiconductor Electronics Multiple Choice Questions

Question 1. In an n-type silicon, which of Ibe following statements is true?

  1. Electrons are majority carriers and trivalent atoms are the dopants
  2. Electrons are minority carriers and pentavalent atoms are dopants
  3. Holes are minority carriers and pentavalent atoms dopants (oi holes are majority carriers and trivalent atoms are dopants
  4. Holes are majority carriers and trivalent atoms are dopants

Answer: 3. Holes are minority carriers and pentavalent atoms dopants (oi holes are majority carriers and trivalent atoms are dopants

Question 2. In an unbiased p-n junction, boles diffuse from the p-region to the n -region because

  1. Free electrons In the n -region attract them f v they move across the junction by the potential difference
  2. They move across the junction by the potential difference
  3. Hole concentration In p -the region is higher as compared To the n-region
  4. All the above

Answer: 3. Hole concentration in p – the region is more as compared To n-region

Question 3. Carbon, silicon, and germanium have four valence electrons each.’ These are characterisedi>y valence and conduction bands separated by energy band gap equal to (£g)c, (£g)s. and (£g)Ge> Which of the following statements is true?

  1. (Eg)Si<(Eg)GeE<(Eg)C
  2. (Eg)C<(Eg)Ge<(Eg)Si
  3. (Eg)C>(Eg)Si>(Eg)Ge
  4. (Eg)C= (Eg)Si= (Eg)Ge

Answer: 3.(Eg)C>(Eg)Si>(Eg)Ge

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Question 4. In V0 is the potential barrier across a p-n junction, when no battery is connected across the junction

Semiconductors And Electrons Potential Barrier pn Juction

  1. 1 and 3 both correspond to the forward bias of the junction
  2. 3 corresponds to the forward bias of the junction and 1 corresponds to the reverse bias of the junction
  3. 1 corresponds to forward bias and 3 corresponds to reverse bias of junction
  4. 3 and 1 both correspond to the reverse bias of the junction

Answer: 2. 3 corresponds to the forward bias of the junction and 1 corresponds to the reverse bias of the junction

Question 5. Assuming the diodes to be ideal

Semiconductors And Electrons Diodes To Be Ideal

  1. D1 is forward-biased and D2 is reverse biased, hence current flows from A to B
  2. D2 is forward biased and D1 is reverse biased, hence n current flows from B to A and vice versa
  3. D1 and D2 are both forward-biased and hence current flows from A to B
  4. D1 and D2, are both reverse biased and hence no current flows from A to B and vice versa

Answer: 2. D2 is forward biased and D1 is reverse biased, hence n current flows from B to A and vice versa

Question 6. A 220 V AC supply is connected between points A and B will be the potential difference V across the capacitor

Semiconductors And Electrons V Across The Capacitor

  1. 220V
  2. 110V
  3. 0V
  4. 222√2V

Answer: 4. 222√2V

Question 7. In the circuit, if the diode forward voltage drop is 0.3 V, the voltage difference between A and B is

Semiconductors And Electrons Diode Forward Voltage Drop

  1. 1.3 V0
  2. 2.3 V
  3. 0
  4. 0.5 V

Answer: 2. 2.3 V

Question 8. The output of the given circuit in

Semiconductors And Electrons Output Of Circuit

  1. Would be zero
  2. Would be like a half-wave rectifier with positive cycles in the output
  3. Would be like a half-wave rectifier with negative cycles in the output
  4. Would be like that of a full-wave rectifier

Answer: 3. Would be like a half-wave rectifier with negative cycles in the output

Question 9. Consider an n-p-n transistor with its base-emitter junction forward-biased and collector-base junction reverse-biased. Which of the following statements is true?

  1. Electrons cross over from emitter to collector
  2. Holes move from base to collector
  3. Electrons move from emitter to base
  4. Electrons from the emitter move out of the base without going to the collector

Answer: 1 And 3

Question 10. The breakdown in a reverse-biased p-n junction is more likely to occur due to the

  1. The large velocity of the minority charge carriers if the doping concentration is small
  2. The large velocity of the minority carriers if the doping concentration is large
  3. The strong electric field in a depletion region if the doping concentration is small
  4. Strong electric field in the depletion region if the doping concentration is large

Answer: 1 And 4

Question 11. In an n-p-n transistor circuit, the collector current is 10 mA. If 95% of the electrons emitted reach the collector, which of the following statements is true?

  1. The emitter current will be 8 mA
  2. The emitter current will be 10.53 mA
  3. The base current will be 0.53 mA
  4. The base current will be 2 mA

Answer: 2 And 3

Question 12. If the potential difference is applied, the value of the electric current

  1. Becomes infinite for an insulator kept at OK
  2. Becomes zero for a semiconductor kept at 0 K
  3. Becomes finite for a metal kept at 0 K
  4. Becomes infinite in a forward-biased p-n junction diode kept at 300 K

Answer: 3. Becomes finite for a metal kept at 0 K

Question 13. Two pieces of copper and germanium are cooled from room temperature to 77 K. As a result,

  1. Resistance of both the pieces will increase
  2. Resistance of both pieces will decrease
  3. Resistance of copper will decrease but that of germanium will increase
  4. Resistance of copper will increase but that of germanium will decrease

Answer: 3. Resistance of copper will decrease but that of germanium will increase

Question 14. For Intrinsic semiconductors, the energy gap of the forbidden zone Is approximately

  1. 0.01 eV
  2. 0.1 eV
  3. 1 eV
  4. 10 eV

Answer: 3. 1 eV

Question 15. In a semiconducting material, the mobilities of electrons and holes are pe and ph respectively. Which of the following is time?

  1. μeh
  2. μeh
  3. μe= μh
  4. μe>< 0 , μh>0

Answer: 1.μeh

Question 16. In some substances, the charge can flow at ordinary temperatures, but not at very low temperatures. These are called

  1. Conductors
  2. Insulators
  3. Semiconductors
  4. Dielectric

Answer: 3. Semiconductors

Question 17. If a small amount of antimony is added to the germanium crystal

  1. It becomes a P-type semiconductor
  2. The antimony becomes an acceptor atom
  3. There will be more free electrons than holes in the semiconductor
  4. Its resistance is increased

Answer: 3. There will be more free electrons than holes in the semiconductor

Question 18. Pure Si at 500K has an equal number of electron (nf) hole (nh) concentrations of 1.5 × 1016.m-3 Doping by indium increases nh to 4.5 × 1022.m-3. The doped semiconductor is of concentration

  1. p-type basing electron concentration ne= 5 × 109.m-3
  2. n-type having electron concentration ne= 5 × 1022.m-3
  3. p-type having electron concentration ne= 2. 5 × 1010.m-3
  4. n-type having electron concentration ne= 2.5 × 1023m-3

Answer: 1. p-type basing electron concentration ne= 5 × 109.m-3

Question 19. A rectifier converts

  1. Mechanical energy in electrical
  2. Liglit energy into electrical
  3. ac to dc
  4. dc to ac

Answer: 3. ac to dc

Question 20. If a p-n junction diode is not connected in a circuit, then

  1. The potential is the same everywhere
  2. The potential of p -end is more than n -end
  3. An electric field acts from the N-end junction
  4. An electric field acts from the p -end to n -end at the junction

Answer: 3. An electric field acts from the N-end junction

Question 21. In the circuit, The forward bias resistances of both the diodes are 50, and reverse bias resistances are infinite. If the battery voltage is 6 V, the current through 100fl resistance in unit A is

Semiconductors And Electrons Diode

  1. Zero
  2. 0.02
  3. 0.03
  4. 0.036

Answer: 2. 0.02

Question 22. Two identical p-n junctions are connected in series with a battery in three different ways. The potential drop across the two p-n junctions will be equal

Semiconductors And Electrons pn Juction are Connected Three are connw

  1. In the circuits 1 and 2
  2. In the circuits 2 and 3
  3. In the circuits 3 and 1
  4. In the circuit 1 only

Answer: 2. In the circuits 2 and 3

Question 23. When a p-n diode is reverse-biased, then

  1. No current flows 20 V 15V 1kft
  2. The depletion region is increased
  3. The depletion region is reduced
  4. The height of the potential barrier is reduced

Answer: 2. The depletion region is increased

Question 24. The current through the given circuit 

Semiconductors And ElectronsCurrent Through The Circuit

  1. \(\frac{3}{10}\) A
  2. \(\frac{1}{10}\) A
  3. \(\frac{3}{50}\) A
  4. \(\frac{3}{10}\) A

Answer: 3. \(\frac{3}{50}\) A

Question 25. The impurity atoms that should be added to germanium to make it n-type of semiconductor is

  1. Iodine
  2. Indium
  3. Arsenic
  4. Aluminium

Answer: 3. Arsenic

Question 26. The circuit has two oppositely connected ideal diodes in parallel. What is the current in the circuit

Semiconductors And Electrons Current In The Circuit

  1. 1.33A
  2. 1.71A
  3. 2.00A
  4. 2.31A

Answer: 3. 2.00A

Question 27. When a p-n junction is reverse-biased, then

  1. No current flows
  2. The depletion layer is increased
  3. The depletion layer is decreased
  4. The height of potential barriers is reduced

Answer: 3. The depletion layer is increased

Question 28. A Zener diode having a breakdown voltage equal to 15Y is used in a voltage regulator circuit. The current through the diode is

Semiconductors And Electrons Current Through The Circuit

  1. 5 mA
  2. 10 mA
  3. 15 mA
  4. 20 mA

Answer: 5mA

Question 29. If the rate of dropping in the emitter, base, and collector of a transistor is De, Db, and De respectively, then

  1. De= Db = Dc
  2. De < Db = Dc
  3. De > Db > Dc
  4. De > Dc > Db

Answer: 4. De > Dc > Db

Question 30. In the active region of a transistor, the biasing at the emitter-base junction and collector-base junction are respectively

  1. Forward, Forward
  2. Forward, Reverse
  3. Reverse, Forward
  4. Reverse, Reverse

Answer: 2. Forward, Reverse

Question 31. A transistor is used as

  1. A rectifier
  2. An amplifier
  3. An oscillator
  4. A source of electrons and holes

Answer:  2. An amplifier

Question 32. In an n-p-n transistor circuit. collector current Is 10 mA. If 90% A of electrons from the emitter enter into the collector then

  1. Emitter current = 11.11 mA
  2. Emitter current
  3. = 9mA
  4. Base current = 2.1 mA
  5. Base current = 0.9 mA

Answer: 1. Emitter current = 11.11 mA

Question 33. For a transistor, if ΔIC/ΔIE = 0.96, then the current gain = β is

  1. 6
  2. 12
  3. 24
  4. 48

Answer: 3. 24

Question 34. A transistor is operated in a common-emitter configuration at Vc = 2V such that a change in the base current from 100 A to 300 A produces a change in the collector current from 10 mA to 20 mA. the current gain is

  1. 50
  2. 75
  3. 100
  4. 25

Answer: 1. 50

Question 35. If the open-loop gain feedback ratio of a positive feedback oscillator is A are r respectively, then the closed-loop gain Af is

  1. 1
  2. <A
  3. <A
  4. Infinity

Answer:  4. Infinity

Question 36. The depletion region of the p-n junction completely vanishes, if.

  1. A suitable forward bias is applied
  2. a suitable reverse bias is applied
  3. a light of suitable frequency is made incident from outside
  4. The Zener effect takes place

Answer:  1,3,4

Question 37. If a pentavalent element is doped in an intrinsic semiconductor, then

  1. a p-type semiconductor is formed
  2. The effective energy gap of the forbidden zone decreases
  3. The energy states of free electrons in  the pentavalent element come nearer to the conduction band
  4. The energy states of free electrons in the pentavalent element come down near the valence band

Answer: 2,3

Question 38. If a p-n junction is reverse-biased, then

  1. A potential barrier is created at the junction
  2. The effective resistance reaches an infinite value
  3. A small current is obtained due to the diffusion of the majority of carrier electrons and holes
  4. Despite increasing the reverse bias, the reverse current remains almost unchanged

Answer:  1,2,3

Question 39. In case of a transfer

  1. The emitter region is heavily doped
  2. In CE configuration, if the base-emitter and the collector-emitter both junctions are forward biased, then the transistor acts in the saturation region
  3. To use as an amplifier, it is operated in the active region
  4. To use as a switch, it is operated in either cut region or saturation region

Answer: 1,2,3,4

Question 40. In case of a Zener diode,

  1. To use as a voltage regulator, it is kept in reverse bias.
  2. Power consumption in reverse bias is higher than that of an ordinary semiconductor diode
  3. On forward bias, _ it behaves as an ordinary semiconductor diode is
  4. If Zeiifer voltage is applied in reverse bias, then a high potential barrier is created at its junction

Answer:  1,2,3

Question 41. In a feedback oscillator

  1. Effective amplification of the amplifier used in this oscillator is infinity
  2. The output AC signal frequency is only determined by the feedback ratio
  3. The output AC signal frequency is controlled by a tank circuit in the feedback device
  4. The output AC signal is obtained without any externally applied input

Answer: 1,3,4

Question 42. In an n-type semiconductor, If n and p am dm WHvmtratlon of electrons and holes respectively and n( Is die concentration, of electron-hole pairs In a pure semi doctor, then

  1. n = p
  2. n>p-
  3. n<p
  4. np = n²1

Answer:  1,3,4

Question 43.  A common-emitter DC circuit of the n-p-n transistor is shown. VBB and VCC are applied emf of the external source at the base end and collector end respectively. Generally, if we need to amplify an AC signal, it is to be applied at the base end. Hence base end is called the input end. RB and IB are input resistance and input DC respectively.

⇒ In most of the cases, input resistance RB is induced due to the internal resistance of the transistor. The amplified signal of the transistor is obtained at the collector end. Thus the col¬lector end is called the output end. Here, RL is external load resistance and IC is the output DC

Semiconductors And Electrons Commn Emitter dc Circuit npn Transistor

The terminal voltage across RL, V0 = ICRL is the output voltage; Vi = IBRB is the input voltage. In the case of only DC biasing of the transistor, the current gain iff = voltage gain β =\(\frac{I_C}{I_B}\), power gain =. \(=\frac{P_o}{P_i}\)

In a given circuit, VCC – 8V, the terminal voltage across load resistance =0.8V, load resistance = 800 Ω, the internal resistance of the transistor = 200 Ω, and βdc – 250.

 1. The value of base current (in μA)

  1. 0.8
  2. 2.5
  3. 4.0
  4. 8.0

Answer:  3. 4.0

 2. The value of collector current (in mA)

  1. 1.0
  2. 2.5
  3. 8.0
  4. 10.0

Answer:  1. 1.0

3. The collector-emitter voltage (in volt)

  1. 2.5
  2. 7.2
  3. 8.0
  4. 8.8

Answer:  2. 7.2

4. Voltage gain

  1. 250
  2. 1000
  3. 2000
  4. 4000

Answer:  2. 1000

5. Power gain

  1. 250
  2. 2500
  3. 25000
  4. 250000

Answer: 4. 250000

Question 44. To maintain a constant potential difference across a regulative load resistance RL, it is not connected directly with an unregulated voltage source Vf. Hence a reverse biased Zener diode may be connected parallel to the load resistance. If the range of the current through the load resistance in which the value ofthe terminal voltage is well maintained within maximum value VQ and minimum value V, then percentage load regulation

r = \(\frac{V_0-V}{V_0} \times 100\)

Each Zener diode has a voltage rating and a watt rating. According to this, the current through the Zener diode has

a specific value above which the Zener diode will be burnt Hence to bypass this damage, an additional resistance R is to be connected in the circuit

Semiconductors And Electrons Specific Value Above Which The Zener Diode

In a given circuit, the maximum voltage of the external unregulated source is 15V, the rating of the Zener diode is 6 V-0.25 W and the maximum and minimum voltages across the load resistance are 5.95 V and 5.90 V respectively.

1. Maximum safe current through the Zener diode is approximately (in mA)

  1. 1.5
  2. 9.0
  3. 24.0
  4. 41.67

Answer: 4. 41.67

2. The minimum value of the resistance R is approximately

  1. 360
  2. 216
  3. 166
  4. 83

Answer: 2. 216

3. Percentage load regulation

  1. 0.84
  2. 4.2
  3. 5.95
  4. 8.4

Answer: 1. 0. 84

Question 45. The impurity atom which when added to germanium makes it an n-type semiconductor

  1. Boron
  2. Indium
  3. Arsenic
  4. Aluminium

Answer: 3. Arsenic

Question 46. What will happenifthe amount of reverse biasing a p-n junction diode is gradually increased?

  1. The thickness of the depletion region will increase
  2. The flow of current due to majority carriers will increase
  3. The thickness of the depletion region will decrease
  4. The flow of current due to majority carriers will decrease

Answer: 1. Thickness of the depletion region will increase

Question 47. For a transistor if β = 100, then α will be

  1. 0.99
  2. 1.01
  3. 100
  4. 0.0

Answer: 1. 0.99

β = \(\frac{\alpha}{1-\alpha}\)

Or, \(\frac{\beta}{1}=\frac{\alpha}{1-\alpha}\)

= \(\frac{\beta}{1+\beta}=\frac{\alpha}{(1-\alpha)+\alpha}\)

∴ α = \(\frac{\beta}{1+\beta}=\frac{100}{1+100}\)

= \(\frac{100}{101}\)

= 0.99

Question 48. The lengths, radii, and specific resistances of two conducting wires are each in the ratio of 1: 3. If the resistance of the thinner wire is 10Ω, then the resistance of the other wire will be

  1. 40 Ω
  2. 20 Ω
  3. 10 Ω
  4. 5 Ω

Answer: 3. 10Ω

We know, R = \(\rho \frac{l}{A}=\frac{\rho l}{\pi r^2}\)

∴ \(\frac{R_1}{R_2}=\frac{\rho_1}{\rho_2} \cdot \frac{l_1}{l_2} \cdot\left(\frac{r_2}{r_1}\right)^2\)

= \(=\frac{1}{3} \times \frac{1}{3} \cdot\left(\frac{3}{1}\right)^2\)

= 1

R2=  R1 =  10

Question 49. Innormal transistor operation

  1. Emitter-base junction and collector-base junction are both in reverse bias
  2. Emitter-base junction is in forward bias and collector base junction is in reverse bias
  3. Emitter-base junction and collector-base junction both are in forward bias
  4. Emitter-base junction is in reverse bias and the collector-base junction is in forward bias

Answer: 2. Emitter-base junction is in forward bias and the collector-base junction is in reverse bias

In the common-base (CB) mode of a transistor, the emitterbase junction is kept at forward bias keeping the base grounded and the collector-base junction is kept at reverse bias to get the proper circuit action.

Question 50. In a transistor output characteristics commonly used in the common-emitter configuration, the base current IB, the collector current IC and the collector-emitter voltage VCE have values of the following orders of the magnitude in the active region

  1. IB and IC are both in μA and VCE in V
  2. IB is in μA, IQ in mA, and VCE in V
  3. IB is in mA, IC in μA, and VCE in mV
  4. IB is in mA, IC is in mA and VCE in mV

Answer: 2. IB is in μA, IQ in mA, and VCE in V

Question 51. In the circuit shown assume the diode to be ideal. When Vf increases from2Vto 6V, the changes in the current is(In mA)

Semiconductors And Electrons The Change In The Current

  1. Zero
  2. 20
  3. 80/3
  4. 40

Answer: 2. 20

When Vi. increases from 2V to 3V, the diode remains in reverse bias, so current I = 0

When Vi increases from 3V to 6V, the current increases From 0 to; so,I = \(\frac{(6-3) V}{150 \Omega}\)= 0.02A

= 20mA

Question 52. If the band gap between the valence band and conduction band in a material is 5.0 eV, then the material

  1. Semiconductor
  2. Good conductors
  3. Superconductor
  4. Insulator

Answer: 4. Insulator

Question 53. Assume that each diode. 1.70 has a forward bias resistance of 50Ω and an infinite reverse bias resistance. The current through the resistance 150Ω is

Semiconductors And Electrons Diode

  1. 0.66 A
  2. 0.05 A
  3. Zero
  4. 0.04 A

Answer: 4. 0.04 A

The uppermost diode in the circuit is forward-biased. But the diode beneath it is reverse biased, hence would not conduct any current

The current through the closed circuit

= \(\frac{10 \mathrm{~V}}{(50+50+50) \Omega}\)

= \(\frac{10}{250}\)

= 0.04A

Question 54. In the case of a bipolar transistor β = 45. The potential drop T across the collector resistance of 1 kΩ is 5 V. The base current is approximately

  1. 22 μA
  2. 55 μA
  3. 11μA
  4. 45 μA

Answer: 3. 11 μA

Here β = 45

∴ \(\frac{I_C}{I_B}\) = 45

Now, IC ×  1 × 10³ = 5 or, IC = 5 × 10-3

∴ \(I_B=\frac{I_C}{45}\)

= \(\frac{5 \times 10^{-3}}{45}\)

= 0.111 × 10-3

= 111 μA

Question 55. A zener diode having breakdown voltage 5.6 Vis connected in reverse bias with a battery ofemf10 V and a resistance of 100 fl in series. The current flowing through the more zen is

  1. 88 mA
  2. 4.4 mA
  3. 0.88 mA
  4. 44 mA

Answer: 4. 44 mA

Semiconductors And Electrons Current Flowing Through The Zener

Her, I= \(\frac{10-5.6}{100}\)

= 0.044 A

= 44 × 10-3

= 44 mA

Question 56. When a semiconductor device is connected in series with a battery and a resistance, a current is found to flow in the circuit. If, however, the polarity of the battery is reversed, practically no current flows in the circuit. The device may be

  1. A p-type semiconductor
  2. A n-type semiconductor
  3. An intrinsic semiconductor
  4. A p-n junction

Answer: 4. A p-n junction

Question 57. What will be the current flowing through the 6kil resistor in the circuit shown, where the breakdown voltage of the Zener is 6 V?

Semiconductors And Electrons Breakdown Voltage Of The Zener

  1. \(\frac{2}{3}\)mA
  2. 1 mA
  3. 10 mA
  4. \(\frac{3}{2}\)mA

Answer: 1. \(\frac{2}{3}\)mA

As the breakdown voltage of Zener is 6v, the potential drop in the 4 kΩ resistor is 6V.

The potential drop in 6 kΩ resistor is 4 V

∴ The current flowing through the 6kΩ resistor

= \(\frac{4}{6 \times 10^3}\) A

= \(\frac{2}{3}\)mA

Question 58. The forward-biased diode connection is

Semiconductors And Electrons Forward Biased Diode Connection

Answer: 1

In the case of forward bias of a p-n junction diode, the potential ofp -side is greater than n -side.

Question 59. Identify the semiconductor devices whose characteristics are given below, in the order (1), (2), (3), (4)

Semiconductors And Electrons Semiconductor Devices

  1. Simple diode, zener diode, solar cell, light-dependent resistance
  2. Zener diode, simple diode, light-dependent resistance, solar cell
  3. Solar cell, light-dependent resistance, zener diode, simple diode
  4. Zener diode, solar cell, simple diode, light-dependent resistance

Answer: 1. Simple diode, zener diode, solar cell, light-dependent resistance

Question 60. For a common emitter configuration,if a and /? have their usual meanings, the incorrect relationship between cr and is

  1. \(\frac{1}{\alpha}=\frac{1}{\beta}+1\)
  2. \(\alpha=\frac{\beta}{1-\beta}\)
  3. \(\alpha=\frac{\beta}{1+\beta}\)
  4. \(\alpha=\frac{\beta^2}{1+\beta^2}\)

Answer: 3. \(\alpha=\frac{\beta}{1+\beta}\)

Question 61. In a common-emitter amplifier circuit using an n-p-n transistor, the phase difference between the input and the output voltages will be

  1. 45°
  2. 90°
  3. 135°
  4. 180°

Answer: 4. 180v

Question 62. The reading of the ammeter for a silicon diode in the given circuit is

Semiconductors And Electrons Ammeter For A Silicon Diode

  1. 11.5 mA
  2. 13.5 mA
  3. 0
  4. 15mA

Answer: 1. 11.5 mA

Semiconductors And Electrons Ammeter For A Silicon Diode

For silicon diode, the stopping potential is 0.7 V

I = \(\frac{V-V_{\text {diode }}}{R}\)

= \(\frac{3-0.7}{200} \times 1000\)

= 11.5 mA

Question 63. The barrier potential of a p-n junction depends on

1. Type of semiconductor material

2. The amount of doping and

3. Temperature. Which one of the following is correct?

  1.  (1) and (2) only
  2. (2) only
  3. (2) and (3) only
  4. (1), (2), and (3)

Answer: 4. (1), (2), and (3)

The barrier potential V of-n junction diode,

  • Is proportional to temperature T increases with the Increase of density of the donor atom and acceptor atom In the two parts of the diode.
  • Decreases with the increase of number density (nÿ) of the thermal electron and hole of the pure semiconductor. This
  • H depends on the material of the semiconductor.

Question 64. The given graph represents V-I characteristics for a semiconductor device. Which ofthe following statements Is correct?

Semiconductors And Electrons VI Characteristic For A Semiconductor

  1. It Is a V-I characteristic for solar cells where point A represents open circuit voltage and point B short circuit current
  2. It is for a solar cell and points A and B represent open circuit voltage and current respectively
  3. It Is for a photodiode and points A and B represent open circuit voltage and current respectively
  4. It is for LED and points A and B represent open circuit voltage and short circuit current respectively

Answer: 1. It Is a V-I characteristic for solar cells where point A represents open circuit voltage and point B short circuit current

Question 65. If p-n junction, a square input signal of 10 V is applied, as shown,

Semiconductors And Electrons p-n Junction A Square Input Signal

Then the output across RL will be

Semiconductors And Electrons pn Junction A Square Input Signal.

Answer: 4

Only positive voltage can pass through a p-n junction diode

Question 66. Consider the junction diode as ideal. The value of current flowing through AB Is

Semiconductors And Electrons Juction Diode As Ideal

  1. 10-2 A
  2. 10-1 A
  3. 10-3 A
  4. 0

Answer: 1. 10-3 A

The p-n junction diode is forward-biased

I = \(\frac{V}{R}=\frac{4-(-6)}{1000}\)

= 10-2 A

Question 67. A n-p-n transistor is connected to a common emitter configuration in a given amplifier. A load resistance of 800 ft is connected in the collector circuit and the voltage drop across it is 0.8 V. If the current amplification factor is 0.96 and the input resistance of the circuit is 192 ft, the voltage gain and the power gain of the amplifier will respectively be

  1. 3.69, 3.84
  2. 4,4
  3. 4,369
  4. 4,3.84

Answer: 4. 4,3.84

Here β =  0.96

RL = 800

V0 = 0.8V

RB = 192Ω

∴ Voltage grain = \(\beta \frac{R_L}{R_n}=0.96 \times \frac{800}{192}\)

= 4

∴ Power gain = \(\beta^2 \frac{R_L}{R_B}=(0.96)^2 \times \frac{800}{192}\)

= 3.84

Question 68. Two sides of a semiconductor germanium crystals A and B are doped with arsenic and indium, respectively. They are connected to a battery. 

Semiconductors And Electrons Semiconductor Germanium Crystal

The correct graph between current and voltage for the arrangement is

Semiconductors And Electrons Graph Between Current And Voltage For The Arrangement

Answer: 1.

Arsenic is a pentavalent sample and indium is a trivalent sample. As side A is doped with arsenic is n-type and as side B is doped with indium it is p-type. Therefore, the circuit is reverse-biased. But the given electric cell is a fixed source. If it is considered as an ideal source then there will be no change in the electromotive force.

Question 69. A common-emitter amplifier circuit is shown in the figure below. For the transistor used in the circuit the current amplification factor, βdc = 100. Other parameters are mentioned.

Semiconductors And Electrons A Common Emitter Amplifier Circuit

We find that

  1. VBE=  . + 18.2 V, VBC = -3.45 V, and the amplifier is  working
  2. VBE = + 18.5 V, VBC =  +2.85 V, and the amplifier is not working
  3. VBE =. + 120.7 V, VBC = + 3.75 V=  and amplifier Is not working
  4. VBE=  . + 21.5 V, VBC = -2.75 V, and the amplifier is  working

Answer: 3. VBE =. + 120.7 V, VBC = + 3.75 V=  and amplifier Is not working

VCE =  VCC – IC RC =  24- (1.5 × 10-3) × (4.7 × 10³)

= 16.95 V

VBE VCC – IB RB =  \(V_{C C}-\frac{I_C}{\beta} R_B\)

= 24 – \(\frac{1.5 \times 10^{-3}}{100} \times\left(220 \times 10^9\right)\)

= 20.7 V

The p – side of the n-p-n transistor i.e the base connected with +20 .7V, means it is kept in forward.

Again, the n-type collector is connected with +16.95 V, which means it is kept in reverse bias.

∴ This transistor is in the active region. So it acts as an amplifier

VBC = VBC + VEC = VBE – VCE

20.7-16.95 = 3.75 V

Question 70. In the circuit shown in the figure, the input voltage V. is 20 V, VB£ = 0 and VCE – 0. The values of IB, Ic, and /? are given by

Semiconductors And Electrons Curcuit The Input Voltage

  1. IB = 20μA, IC= 5 mA, β = 250
  2. IB = 25μA, IC = 5 mA, β = 200
  3.  IB = 40 μA, IC= 5 mA, β = 250
  4.  IB = 40μM, IC= 5 mA, β = 125

Answer: 4.  IB = 40μM, Ic = 5 mA, β = 125

Applying KVL in loop ABEKD we get,

500 × l0³ IB + VBE-20 = 0

Or, \(=\frac{20}{5 \times 10^5}\)

= 40 μA

Semiconductors And Electrons Circuit The Input Voltage

Applying KVL in loop FGHKEBC we get

⇒ \(4 \times 10^3 I_C+V_{C E}-20\) = 0

⇒ \(I_C=\frac{20}{4 \times 10^3}\)

= 5 mA

Or, IC= βIB

Or, β = \(\frac{I_C}{I_B}=\frac{5 \times 10^{-3}}{40 \times 10^{-6}}\)

= 125

Question 71. Inap-w junction diode, changeintemperaturedue to heating

  1. Does not affect the resistance of the p-n junction
  2. Affects only forward resistance
  3. Affects only reverse resistance
  4. Affects the overall V-I characteristics of the p-n junction

Answer: 4. Affects the overall V-I characteristics of the p-n junction

The number density of electrons and holes of a p-n junction diode increases due to heating. So, the characteristics graph of the p-n junction diode will change totally

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