Semiconductor Electronics, Materials, Devices and Simple Circuits

Semiconductor Electronics: Materials, Devices and Simple Circuits Class 12 MCQs Questions with Answers

Question 1.
In a semiconductor, the forbidden energy gap between the valence band and the conduction band is of the order of:
(a) 1 Mev
(b) 1 ev
(c) 0.1 Mev
(d) 5ev

Question 2.
If the conductivity of a semiconductor is only due to break of the covalent band due to the thermal excitation, then the semiconductor is called:
(a) intrinsic
(b) extrinsic
(c) Acceptor
(d) none of these

Question 3.
In a good conductor, the energy levels in a valence band:
(a) are partially filled only.
(b) overlap with conduction band only.
(c) both (a) and (b) are correct.
(d) none of these

Question 4.
A hole in a p-type semiconductor is-
(a) an excess electron
(b) A missing atom
(c) A missing electron
(d) A donor level.

Question 5.
The mobility of conduction electrons is greater than that of holes since electrons is greater than that of holes since electrons.
(a) are negatively charged.
(b) are lighter
(c) require smaller energy for moving through the crystal lattice.
(d) Undergo smaller number of collisions.

Question 6.
The Voltage gain is highest for
(a) common emitter amplifier
(b) common base amplifier
(c) common collector amplifier.
(d) Equal in all the three.

Question 7.
In an n-p-n transistor circuit the collector current is 18 mA. If 90% of the electrons emitted reach the collector, than the emitter current is:
(a) 1.6 mA
(b) 16.4 mA
(c) 18 mA
(d) 20 mA

Question 8.
In the common emitter amplifier, the phase difference between the input voltage and output voltage signal across the collector and emitter is:
(a) 0
(b)π/2
(c) π
(d)π/4

Question 9.
In common base amplifier, the phase difference between the input and output voltage signal is
(a) 0
(b) π/2
(c) π/4
(d) π

Question 10.
The part of the transistor which is heavily doped to produce a large number of majority carriers is:
(a) emitter
(b) base
(c) collector
(d) none

Question 11.
In principle, Boolean algerbra is based on:
(a) simple numbers
(b) binary numbers
(c) logic
(d) truth

Question 12.
The following logic symbol is equivalent to:

(a) AND gate
(b) OR gate
(c) NOT gate
(d) NAND gate

Question 13.
Which of the following gates corresponds to the truth table given here:

(a) NAND
(b) OR
(c) NOR
(d) AND

Question 14.
The conductivity of semiconductors like Ge and Si:
(a) increases when it is doped with pentavalent impurity.
(b) increases when it is doped with trivalent impurity.
(c) increases when it is doped with pentavalent or trivalent impurity.
(d) none

Question 15.
In which case is the junction diode forward biased.

Question 16.
Assuming that the junction diode is ideal, the current in the arrangement shown here is:

(a) 2 mA
(b) 30 mA
(c) 20 mA
(d) 10 mA

Question 17.
An oscillator is an amplifier with:
(a) a large gain
(b) Negative feedback
(c) positive feedback
(d) no feedback

Question 18.
How many AND gates are required to form, NAND gate?
(a) 0
(b) 1
(c) 2
(d) 4

Question 19.
Which of following statements is not true?
(a) Resistance of an intrinsic semiconductor decreases with increase in temperature.
(b) Doping pure Si with trivalent impurities gives p-type semiconductor.
(c) The majority carriers in n-type semiconductor are holes.
(d) A p-n junction can act as semiconductor diode.

Question 20.
For a transistor, current amplification factor is 0.8. The transistor is changed to common emitter configuration. For a change of 6 mA in base current. Change in collector current is
(a) 4.8 mA
(b) 6 mA
(b) 8 mA
(d) 24 mA

Question 21.
A truth table is given below. Which of the following has this type of truth table?

(a) XOR gate
(b) NOR gate
(b) AND gate
(d) OR gate

Question 22.
Bonds in a semiconductor :
(a) trivalent
(b) covalent
(c) bivalent
(d) monovalent

Question 23.
Number of electrons in the valence shell of a semiconductor is:
(a) 1
(b) 2
(c) 3
(d) 4

Question 24.
Semiconductors of both p-type and n-type are produced by:
(a) ionic solids
(b) covalent solids
(c) metallic solids
(d) molecular solids

Question 25.
With fall of temperature, the forbidden energy gap of a semiconductor
(a) increases
(b) decreases
(c) sometimes increases and sometimes decreases
(d) remains unchanged

Question 26.
In a p-type semiconductor, current conduction is by:
(a) atoms
(b) holes
(c) electrons
(d) protons

Question 27.
The relation between number of free electrons (n) in a semiconductor and temperature (T) is given by:
(a) n ∝ T
(b) n ∝ T²
(c) n ∝ T^1/2
(d) n ∝ T^3/2

Question 28.
In reverse biasing:
(a) large amount of current flows
(b) no current flows
(c) potential barrier across junction increases
(d) depletion layer resistance increases

Question 29.
Main function of a transistor is to :
(a) rectify
(b) simplify
(c) amplify
(d) all the above

Question 30.
To obtain p-type silicon semiconductor, we need to dope pure silicon with:
(a) aluminium
(b) phosphorus
(c) oxygen
(d)germanium

Question 31.
On applying reverse bias to a junction diode, it:
(a) lowers the potential barrier
(b) raise the potential barrier
(c) increases the majority carrier current
(d) increases the minority carrier current

Question 32.
For germanium crystal, the forbidden energy gap in joules
(a) 1.216 × 10^-19
(b) 1.76 × 10^-19
(c) 1.6 × 10^-19
(d) zero

Question 33.
To obtain electrons as majority charge carriers in a semiconductors the impurity mixed is:
(a) monovalent
(b) divalent
(c) trivalent
(d) pentavalent

Question 34.
In the middle of the depletion layer of a reverse biased p-n junction, the:
(a) electric field is zero
(b) potential is maximum
(c) electric field is maximum
(d) potential zero.

Question 35.
In a common base amplifier the phase difference between the input signal voltage and output voltage is :
(a) π/2
(b) 0
(c) π/4
(d) π

Question 36.
Energy bands in solids are a consequence of:
(a) Ohm’s Law
(b) Pauli’s exclusion principle
(c) Bohr’s theory
(d) Heisenberg’s uncertainty principle

Question 37.
In semi conductor which are responsible for conduction:
(a) only electron
(b) electron and hole both
(c) only hole
(d) None of these

Question 38.
In binary system III represents:
(a) 1
(b) 3
(c) 7
(d) 100

Question 39.
On heating, resistance of semiconductors:
(a) decreases
(b) increases
(c) remains same
(d) first increases then decreases

Question 40.
p-n junction diode can be used as:
(a) amplifier
(b) oscillator
(c) detector
(d) modulator

Question 41.
In intrinsic semiconductor at room temperature, the number of electrons and holes are:
(a) equal
(b) unequal
(c) infinite
(d) zero

Question 42.
In full wave rectifier, input a.c. current has a frequency v. The output frequency of current is :
(a) V/2
(b) V
(c) 2V
(d) None

Question 43.
Winch of the following gate is not an universal gate?
(a) OR
(b) NOT
(c) AND
(d) NAND

Question 44.
Zener diode is used for:
(a) producing oscillations in a oscillator
(b) amplification
(c) stabilisation
(d) rectification

Question 45.
In semi conductor, at room temperature :
(a) the valence bond is partially empty and the conduction band is partially filled
(b) the valence band is completely filled and the conduction band is partially filled
(c) the valence band is completely filled
(d) the conduction band is completely empty

Question 46.
Crystal diode is:
(a) amplifying device
(b) fluctuating device
(c) non-linear device
(d) linear device

Question 47.
The part of a transistor which is heavily doped to produce a large number of majority carriers is :
(a) base
(b) emitter
(c) collector
(d) None of these

Question 48.
A p-type semiconductor is:
(a) negatively charged
(b) positively charged
(c) uncharged
(d) None of these

Question 49.
The material most commonly used to manufacture electronic solid state devices is :
(a) copper
(b) silicon
(c) germanium
(d) aluminium

Question 50.
What is the number of possible crystal systems?
(a) 5
(b) 7
(c) 14
(d) 16

Fill in the Blanks

Question 1.
…………………. is called as junction in p-n junction diode.

Question 2.
The thickness of the depletion layer is of the order of ………………….

Question 3.
The potential barrier for S₁ is about …………………. and the electric field across the junction is about ………………….

Question 4.
The width of the depletion layer and the potential barrier across the junction …………………. due to reverse biasing.

Question 5.
The direction of conventional current in a p-n junction is from …………………. when it is forward biased.

Question 6.
The zener voltage can have value from …………………. to …………………. volts.

Question 7.
The arrow in the symbol of a transistor shows the direction ………………….

Question 8.
Below knee voltage, the variation of current in the p-n junction is …………………. and above it, it is ………………….

Question 9.
Various components such as resistors, inductors, capacitors, transistors, diodes and logic-gates etc. are grown over one ………………….

Question 10.
…………………. is the most developing area where semiconductors are used.

Question 11.
1 and 0 are called ………………….

Question 12.
The connection between logic and mathematics was realised by …………………. and the algebra developed by him based on 0 and 1 is called ………………….

Question 13.
When a p-n junction is forward biased, then the motion of charge carriers across the barrier is due to …………………. and when it is reversed biased, then the motion of charge carriers is due to ………………….

Question 14.
Digital circuits can be obtained by repetitive use of …………………. gates and are called digital building blocks.

Question 15.
In a digital circuit, the diodes and transistors are operated by a 5V supply. The states 1 and 0 will correspond to …………………. V and …………………. V respectively.

Question 16.
In insulator, the valence elctrons form a band that is ………………….

Question 17.
In the band structure of an intrinsic semiconductor is located ………………….

Question 18.
The region near the junction of pn—diode where there are no charge carriers is called ………………….

Question 19.
A small impurity is added to Ge to get a p-type semiconductor and this impurity is called ………………….

Question 20.
The Boolean expression for AND gate is ………………….

Question 21.
The current gain of common emitter transistor amplifier is …………………. than one and …………………. one for common base amplifier.