# MCQ Questions for Class 12 Physics Chapter 14 Semiconductor Electronics: Materials, Devices and Simple Circuits with Answers

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## 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

Answer

Answer: (b) 1 ev

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

Answer

Answer: (a) intrinsic

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

Answer

Answer: (c) both (a) and (b) are correct.

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.

Answer

Answer: (c) A missing electron

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.

Answer

Answer: (c) require smaller energy for moving through the crystal lattice.

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.

Answer

Answer: (a) common emitter amplifier

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

Answer

Answer: (c) 18 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) $$\frac {π}{2}$$
(c) π
(d) $$\frac {π}{4}$$

Answer

Answer: (c) π

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

Answer

Answer: (a) 0

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

Answer

Answer: (a) emitter

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

Answer

Answer: (c) logic

Question 12.
The following logic symbol is equivalent to:

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

Answer

Answer: (a) AND gate

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

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

Answer

Answer: (a) NAND

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

Answer

Answer: (c) increases when it is doped with pentavalent or trivalent impurity.

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

Answer

Answer: (b)

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

Answer

Answer: (c) 20 mA

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

Answer

Answer: (c) positive feedback

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

Answer

Answer: (b) 1

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.

Answer

Answer: (c) The majority carriers in n-type semiconductor are holes.

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

Answer

Answer: (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

Answer

Answer: (b) NOR gate

Fill in the Blanks

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

Answer

Answer: The surface of contact of p-type and n-type crystal.

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

Answer

Answer: 1 µm = 10-6 m.

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

Answer

Answer: 0.7V, 7 × 103Vm-1

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

Answer

Answer: increases.

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

Answer

Answer: p to n region.

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

Answer

Answer: 1V, several hundred.

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

Answer

Answer: Conventional current or hole current.

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

Answer

Answer: non-linear, linear.

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

Answer

Answer: Semiconductor chip

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

Answer

Answer: Computer

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

Answer

Answer: bits.

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

Answer

Answer: Boole, Boolean Algebra.

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 ………………….

Answer

Answer: diffusion, drift.

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

Answer

Answer: NAND and NOR

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.

Answer

Answer: 5, 0

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

Answer

Answer: valence band which is filled completely.

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

Answer

Answer: midway between the valence band and the conduction band.

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

Answer

Answer: depletion region

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

Answer

Answer: trivalent.

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

Answer

Answer: y = A.B

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

Answer

Answer: more, less.

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