JEE Questions for Physics Semiconductor Devices Quiz 6 - MCQExams.com

A Ge specimen is doped with Al. The concentration of acceptor atoms is 1021 atoms/m3. Given that the intrinsic concentration of electron-hole pairs is 1019/m3 , the concentration of electrons in the specimen is
  • 1017/ m3
  • 1015/ m3
  • 104/ m3
  • 102/ m3
Copper has face centered cubic (fcc) lattice with interatomic spacing equal to 2.54 Ǻ. The value of lattice constant for this lattice is
  • 3.59 Å
  • 2.54 Å
  • 1.27 Å
  • 5.08 Å
In a common base amplifier, the phase difference between the input signal voltage and output voltage is

  • Physics-Semiconductor Devices-87594.png
  • 0
  • π

  • Physics-Semiconductor Devices-87595.png
Which of the following logic gates is an universal gate?
  • OR
  • NOT
  • AND
  • NAND
Identify the property of which is not characteristic for a semiconductor?
  • At a very low temperature, it behaves like an insulator
  • At higher temperatures two types of charge carriers will cause conductivity
  • The charge carriers are electrons and holes in the valence band at higher temperature
  • The semiconductor is electrically neutral
If De = Db and Dc are the doping levels of emitter, base and collector respectively of a transistor, then
  • De = Db = Dc
  • De < Db = Dc
  • De > Db > Dc
  • De < Db < Dc
  • De > Dc > Db
In the diode circuit.
  • D1 and D2 are reverse biased
  • D1 and D2 are forward biased
  • D1 is forward biased and D2 is reverse biased
  • D1 is reverse biased and D2 is forward biased
  • D1 and D2 will not conduct
In a common emitter amplifier, using output resistance of 5000 Ω and input resistance of 2000 Ω, if the peak value of input signal voltage is 10 mV and β = 50, then peak value of output voltage is
  • 5 × 10–6 V
  • 12.50 × 10–4 V
  • 1.25 V
  • 125.0 V
The amplification factor of a triode valve is 120. The current is 6 mA at plate potential, 260 V and grid potential -4V. The valve of plate current (in mA), at plate potential 12 V and grid potential -2 V will be

  • Physics-Semiconductor Devices-87597.png
  • 2)
    Physics-Semiconductor Devices-87598.png

  • Physics-Semiconductor Devices-87599.png

  • Physics-Semiconductor Devices-87600.png
The length of germanium rod is 0.928 cm and its area of cross-section is 1 mm2. If for germanium ni × 25 × 1019 m-3 , μ = 0.19 m2/ V - s, μe = 0.39 m2/ V - s, then the resistance of rod is
  • 2.5 kΩ
  • 4.0 kΩ
  • 5.0 kΩ
  • 10.0 kΩ
At ordinary temperature, an increase in temperature increases the conductivity of
  • conductor
  • insulator
  • semiconductor
  • alloy
If ne and nh are the number of electrons and holes in a semiconductor heavily doped with phosphorous, then
  • ne >> nh
  • ne << nh
  • ne ≤ nh
  • ne = nh
The width of a depletion layer in a p-n junction is
  • increased by reverse biasing
  • is independent of voltage
  • increased by forward biasing
  • decreased by reverse biasing
Which is true about the following?
I. An amplifier is necessarily an oscillator too
II. An oscillator is necessarily an amplifier too
  • only I is correct
  • Only II is correct
  • None of the two is correct
  • Both are correct
In the presence of space charge in the diode valve the plate current is 10 mA at the plate voltage 50 V. Then the plate current at plate voltages 200 V will be
  • 20 mA
  • 40 mA
  • 80 mA
  • none of the above
A transistor oscillator is
(i) an amplifier with positive feedback
(ii) an amplifier with reduced gain
(iii) the one in which D.0 supply energy is converted into an output energy.
Then
  • All (i), (ii) and (iii) are correct
  • Only (i) and (ii) are correct
  • Only (i) and (ii) are correct
  • Only (ii) and (iii) are correct
  • Only (ii) is correct
For a cubic crystal structure which one of the following relations indicating the cell characteristic is correct?
  • a ≠ b ≠ c and α ≠ β and γ ≠ 90°
  • a ≠ b ≠ c and α = β = γ = 90°
  • a = b = c and α ≠ β ≠ γ = 90°
  • a = b = c and α = β = γ = 90°
In a transistor output characteristics commonly used in common emitter configuration, the base current IB the collector current IC and the collector-emitter voltage VCE have values of the following orders of magnitude in the active region
  • IB and IC both are in μA and VCE in volt
  • IB is in μA and IC in mA and VCE in volt
  • IB is in mA and IC is in μA and VCE in mV
  • IB is in mA and IC is in mA and VCE to mV
In a Bipolar Junction Transistor (BJT), the current gain is defined as,
  • The ratio of the change in collector current to the change in emitter current for a constant collector voltage in the common base configuration
  • The ratio of change in collector current to the change in base current for constant collector voltage in CE configuration
  • The ratio of change in emitter current to the change in base current for constant emitter voltage in common emitter configuration
  • The ratio of change in base current to the change in collector current for constant collector voltage in CE configuration
For a transistor amplifier, the voltage gain
  • is high at high and low frequencies and constant in the middle frequency range
  • is low at high and low frequency and constant in the middle frequency range
  • remains constant for all frequencies
  • is high at high frequencies and low at low frequencies and constant in middle frequency range
A working transistor with its three legs marked P, Q and R is tested using a multimeter. No conduction is found between P and Q. By connecting the common (negative) terminal of the multimeter to R and the other (positive) terminal to P or Q, some resistance is seen on the multimeter. Which of the following is true for the transistor?
  • It is an n-p-n transistor with R as base
  • It is a p-n-p transistor with R as collector
  • It is a p-n-p transistor with R as emitter
  • It is an n-p-n transistor with R as collector
Consider a p-n junction as a capacitor, formed with p and n materials acting as thin metal electrodes and depletion layer width acting as separation between them. Basing on this, assume that a n -p-n transistor, is working as an amplifier in CE configuration. If C1 and C2 are the base-emitter and collector-emitter junction capacitances, then
  • C1 > C2
  • C1 < C2
  • C1 = C2
  • C1 = C2 = 0
Which of the following is correct, about doping in a transistor?
  • Emitter is lightly doped, collector is heavily doped and base is moderately doped
  • Emitter is lightly doped, collector is moderately doped and base is heavily doped
  • Emitter is heavily doped, collector is lightly doped and base is moderately doped
  • Emitter is heavily doped, collector is moderately doped and base is lightly doped
The current voltage relation of diode is given by I = (e1000V/T –mA, where the applied voltage V is in volt and the temperature T is in kelvin. If a student makes an error measuring ± 0.01V while measuring the current of 5 mA at 300 K, what will be the error in the value of current in mA?
  • 0.02 mA
  • 0.5 mA
  • 0.2 mA
  • 0.05 mA
Two identical p-n junction are connected in series with battery in three ways. The potential difference across the two p-n junction are equal in
Physics-Semiconductor Devices-87604.png
  • circuit 1 and circuit 2
  • circuit 2 and circuit 3
  • circuit 1 and circuit 3
  • circuit 1 only
In a p-n junction diode are not connected to any circuit
  • the potential is the same everywhere
  • the p-type side has a higher potential than the n-type side
  • there is an electric field at the junction directed from the n-type side to p-type side
  • there is an electric field at the junction directed from the p-type side to n-type side
A p-n junction diode (D) shown in the figure, can act as a rectifier. An alternating current source (V) is connected in the circuit.
Physics-Semiconductor Devices-87605.png

  • Physics-Semiconductor Devices-87606.png
  • 2)
    Physics-Semiconductor Devices-87607.png

  • Physics-Semiconductor Devices-87608.png

  • Physics-Semiconductor Devices-87609.png
Which of the following statements is not correct when a junction diode is in forward bias?
  • The width of depletion region decreases.
  • Free electrons on n -side will move towards the junction.
  • Holes on p -side move towards the junction.
  • Electron on n -side and holes on p -side will move away from junction.
A p-n junction has acceptor impurity concentration of 17 cm-3 in the P side and donor impurity concentration of 1016 cm-3 in the N side. What is the contact potential at the junction? (kT = thermal energy, intrinsic carrier concentration ni = 1.4 × 1016 cm-3 )

  • Physics-Semiconductor Devices-87610.png
  • 2)
    Physics-Semiconductor Devices-87611.png

  • Physics-Semiconductor Devices-87612.png

  • Physics-Semiconductor Devices-87613.png
A zener diode has a contact potential of 1 V in the absence of biasing. It undergoes Zener breakdown for an electric field of 106 V-m-1 at the depletion region of p-n junction. If the width of the depletion region is 2.5 µm, what should be the reverse biased potential for the Zener breakdown to occur?
  • 3.5 V
  • 2.5 V
  • 1.5 V
  • 0.5 V
Carbon, silicon and germanium have four valence electrons each. At room temperature which one of the following statements is most appropriate?
  • The number of free conduction electrons is significant in C but small in Si and Ge
  • The number of free conduction electrons is negligibly small in all the three
  • The number of free electrons for conduction is significant in all the three
  • The number of free electrons for conduction is significant only in Si and Ge but small in C
If the lattice constant of this semiconductor is decreased, then which of the following is correct?
Physics-Semiconductor Devices-87615.png
  • All Ec , Eg , Ev increase
  • Ec and Ev increase ,but Eg decreases
  • Ec and Ev decrease ,but Eg increases
  • All Ec , Eg , Ev decreases
A silicon specimen is made into a p-type semiconductor by doping, on an average, one indium atom per 5 × 107 silicon atoms. If the number density of atoms in the silicon specimen is 5 × 1028 atom-cm-3 , then the number of acceptor atoms in silicon per cubic centimetre will be
  • 2.5 × 1030 atom-cm-3
  • 2.5 × 1035 atom-cm-3
  • 1 × 1013 atom-cm-3
  • 1 × 1015 atom-cm-3
  • None of these
Carbon,silicon and germanium atoms have four valence electrons each. Their valence and conduction bands are separated by energy band gaps represented by (Eg )C , (Eg )Si and (Eg )Ge respectively. Which one of the following relationships is true in their case ?
  • (Eg )C > (Eg )Si
  • (Eg )C = (Eg )Si
  • (Eg )C < (Eg )Ge
  • (Eg )C < (Eg )Si
A p-n junction in series with a resistance of 5 kΩ is connected across a 50 V DC source. If the forward bias resistance of the function is 50 Ω, the forward bias current is
  • 8.8 mA
  • 1 mA
  • 2 mA
  • 20 mA
  • 9.9 mA
Truth table for system of four NAND gate as shown in figure is
Physics-Semiconductor Devices-87617.png

  • Physics-Semiconductor Devices-87618.png
  • 2)
    Physics-Semiconductor Devices-87619.png

  • Physics-Semiconductor Devices-87620.png

  • Physics-Semiconductor Devices-87621.png
The output of given logic circuit is
Physics-Semiconductor Devices-87622.png

  • Physics-Semiconductor Devices-87623.png
  • 2)
    Physics-Semiconductor Devices-87624.png

  • Physics-Semiconductor Devices-87625.png

  • Physics-Semiconductor Devices-87626.png
The real time variation of input signals A and B are as shown below. If the inputs are fed into NAND gate, then select the output signal from the following
Physics-Semiconductor Devices-87627.png

  • Physics-Semiconductor Devices-87628.png
  • 2)
    Physics-Semiconductor Devices-87629.png

  • Physics-Semiconductor Devices-87630.png

  • Physics-Semiconductor Devices-87631.png

  • Physics-Semiconductor Devices-87632.png
The following figure shows a logic gate circuit with two inputs A and B and the output C. The voltage waveforms of A, B and C are as shown below
Physics-Semiconductor Devices-87633.png
  • AND gate
  • NAND gate
  • NOR gate
  • OR gate
Different voltages are applied across a p-n junction and the currents are measured from each value. Which of the following graphs is obtained between voltage and current?

  • Physics-Semiconductor Devices-87634.png
  • 2)
    Physics-Semiconductor Devices-87635.png

  • Physics-Semiconductor Devices-87636.png

  • Physics-Semiconductor Devices-87637.png
The relation between the energy Ef of Fermi level, height Eb of potential barrier and work function Wo is
  • Ef = Wo + Eb
  • Eb = Wo – Ef
  • Eb = Wo + Ef
  • Wo = Eb + Ef
If the height of potential barrier in a metal is Eb and Fermi energy is Ef, then the minimum energy to remove an electron from the metal will be
  • Ef / Eb
  • Ef × Eb
  • Ef + Eb
  • Eb – Ef
In a triode valve
  • if the grid voltage is zero then plate current is zero
  • if the temperature of filament is doubled, then the thermionic current will also be doubled
  • if the temperature of filament is doubled, then the thermionic current will nearly be four times
  • at a definite grid voltage the plate current varies with plate voltage according to Ohm’s law
The value of plate resistance of a triode is 3 × 103 Ω and its mutual conductance factor is 1.5 millimho, then its amplification factor will be
  • 2 × 106
  • 45
  • 4.5
  • 4 × 10–5
If the amplification factor of a triode valve is 100, then at plate potential of 250 volt the cut off voltage of its grid will be
  • 0 V
  • – 0.4 V
  • – 2.5 V
  • – 150 V
When the plate voltage of a triode is 150 V, its cut off voltage is –5V. On increasing the plate voltage to 200 V, the cut off voltage can be
  • – 4.5 V
  • – 5.0 V
  • – 2.3 V
  • – 6.66 V
In vacuum diode for plate potential is gradually varied from – 200 V to 200 V. How will the plate current vary?
  • First increase then decrease
  • First decrease then increase
  • First remain zero, then continuously increases and may cease to vary at higher potential
  • The variation will be different than that described above
At a constant plate potential, if the grid is moved closer to the plate, the amplification factor of triode
  • Decreases
  • Increases
  • Remains unchanged
  • May increase or decrease depending upon grid bias
Which of the following is a crystalline solid?
  • Graphite
  • Calcite
  • Gallium
  • Oxygen
Atomic packing factor for a force centred cubic cell is

  • Physics-Semiconductor Devices-87642.png
  • 2)
    Physics-Semiconductor Devices-87643.png

  • Physics-Semiconductor Devices-87644.png

  • Physics-Semiconductor Devices-87645.png
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