CBSE Class 12 Physics Semiconductor Electronics Materials Devices and Simple Circuits MCQs

Question : The transistor are usually made of 
(a) metal oxides with high temperature coefficient of resistivity
(b) metals with high temperature coefficient of resistivity
(c) metals with low temperature coefficient of resistivity
(d) semiconducting materials having low temperature coefficient of resistivity
Answer: A

Question :   To use a transistor as an amplifier, emitter-base junction is kept in ...X... and base-collector junction is kept in ...Y... Here, X and Y refer to
(a) forward bias, forward bias
(b) reverse bias, reverse bias
(c) reverse bias, forward bias
(d) forward bias, reverse bias
Answer: D

Question : A transistor has three impurity regions. All the three regions have different doping levels. In order of increasing doping level, the regions are
(a) emitter, base and collector
(b) collector, base and emitter
(c) base, emitter and collector
(d) base, collector and emitter
Answer: D

Question : When npn transistor is used as an amplifier
(a) electrons move from collector to base
(b) holes move from emitter to base
(c) electrons move from base to collector
(d) holes move from base to emitter
Answer: D

Question : For a common base amplifier, the values of resistance gain and voltage gain are 3000 and 2800 respectively. The current gain will be
(a) 1.1
(b) 0.98
(c) 0.93
(d) 0.83
Answer: C

Question : The current gain of a transistor in common base mode is 0.995. The current gain of the same transistor in common emitter mode is
(a) 197
(b) 201
(c) 198
(d) 199
Answer: D

Question : In Boolean algebra, Y = A + B implies that
(a) output Y exists when both inputs A and B exist
(b) output Y exists when either input A exists or input B exists or both inputs A and B exist
(c) output Y exists when either input A exists or input B exists but not when both inputs A and B exist
(d) output Y exists when both inputs A and B exists but not when either input A or B exist
Answer: A

Question : NAND and NOR gates are called universal gates primarily because they
(a) are available universally
(b) can be combined to produce OR, AND and NOT gates
(c) are widely used in Integrated circuit packages
(d) are easiest to manufacture
Answer: B 

Question : The gate for which output is high if atleast one input is low?
(a) NAND
(b) NOR
(c) AND
(d) OR
Answer: D 

Question : Hole in semiconductor is
(a) an anti – particle of electron
(b) a vacancy created when an electron leaves a covalent bond
(c) absence of free electrons
(d) an artificially created particle
Answer: D

Question : In a semiconductor
(a) there are no free electrons at 0 K
(b) there are no free electrons at any temperature
(c) the number of free electrons increases with pressure
(d) the number of fre electrons is more than that in a conductor
Answer : A

Question : The electrical conductivity of pure germanium can be increased by
(a) increasing the temperature
(b) doping acceptor impurities
(c) doping donor impurities
(d) All of the above
Answer : D

Question : Electric conduction in a semiconductor takes place due to
(a) electrons only
(b) holes only
(c) both electrons and holes
(d) neither electrons nor holes
Answer : C

Question :  The drift current in a p-n junction is from the
(a) n-side to the p-side
(b) p-side to the n-side
(c) n-side to the p-side if the junction is forward-biased and in the opposite direction if it is reverse biased
(d) p-side to the n-side if the junction is forward-biased and in the opposite direction if it is reverse-biased
Answer : A

Question : If a small amount of antimony is added to germanium crystal
(a) it becomes a p–type semiconductor
(b) the antimony becomes an acceptor atom
(c) there will be more free electrons than holes in the semiconductor
(d) its resistance is increased
Answer : C

Question :  The peak voltage in the output of a half-wave diode rectifier fed with a sinusoidal signal without filter is 10V. The d.c. component of the output voltage is
(a) 20/p V
(b) 10/Ö2 V
(c) 10/p V
(d) 10V
Answer : C

Question : In the half wave rectifier circuit operating from 50 Hz mains frequency, the fundamental frequency in the ripple would be
(a) 25 Hz
(b) 50 Hz
(c) 70.7 Hz
(d) 100 Hz
Answer : B

Question : If the forward bias on p-n junction is increased from zero to 0.045 V, then no current flows in the circuit. The contact potential of junction i.e. VB is
(a) zero                   
(b) 0.045 V
(c) more than 0.045 V
(d) less than 0.045 V
Answer : C

Question : Choose the correct option
Assertion : A pure semiconductor has negative temperature coefficient of resistance.
Reason : In a semiconductor on raising the temperature, more charge carriers are released, conductance increases and resistance decreases.
(a) Assertion is correct, reason is correct; reason is a correct explanation for assertion.
(b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion
(c) Assertion is correct, reason is incorrect
(d) Assertion is incorrect, reason is correct.
Answer : A

Question : An electric field is applied to a semiconductor. Let the number of charge carriers be n and the average drift speed be v. If the temperature is increased
(a) both n and v will increase
(b) n will increase but v will decrease
(c) v will increase but n will decrease
(d) both n and v will decrease
Answer : A