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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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