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NCERT Solutions for class 12 Physics | Chapter 14 - Semiconductor Electronics

(1) A p-type semiconductor is:
[A] negatively charged3
[B] positively charged
[C] uncharged
[D] None of these
Answer: uncharged
(2) Zener diode is used for:
[A] producing oscillations in a oscillator
[B] amplification
[C] stabilisation
[D] rectification
Answer: stabilisation

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(3) 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
Answer: 2V
(4) 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
Answer: the valence bond is partially empty and the conduction band is partially filled
(5) Bonds in a semiconductor :
[A] trivalent
[B] covalent
[C] bivalent
[D] monovalent
Answer: covalent
(6) 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
Answer: emitter
(7) What is the number of possible crystal systems?
[A] 5
[B] 7
[C] 14
[D] 16
Answer: 7
(8) The cause of the potential barrier in a p-n junction diode is
[A] depletion of positive charges near the junction3
[B] concentration of positive charges near the junction
[C] depletion of negative charges near the junction
[D] concentration of positive and negative charges near the junction
Answer: concentration of positive and negative charges near the junction
(9) Reverse bias applied to a junction diode
[A] increases the minority carrier current
[B] lowers the potential barrier
[C] raises the potential barrier
[D] increases the majority carrier current
Answer: raises the potential barrier
(10) In a semiconductor diode, the barrier potential offers opposition to
[A] holes in P-region only
[B] free electrons in N-region only
[C] majority carriers in both regions
[D] majority as well as minority carriers in both regions
Answer: majority carriers in both regions
(11) Filter circuit
[A] eliminates a.c. component
[B] eliminates d.c. component
[C] does not eliminate a.c. component
[D] None of these
Answer: eliminates a.c. component
(12) In V-I characteristic of a p-n junction, reverse biasing results in
[A] leakage current
[B] the current barrier across junction increases
[C] no flow of current
[D] large current
Answer: leakage current
(13) Diffusion current in a p-n junction is greater than the drift current in magnitude)
[A] if the junction is forward-biased
[B] if the junction is reverse-biased
[C] if the junction is unbiased
[D] in no case
Answer: if the junction is forward-biased
(14) 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: n-side to the p-side
(15) A semiconductor device is connected in a series circuit with a battery and a resistance. A current is found to pass through the circuit. If the polarity of the battery is reversed, the current drops to almost zero. The device may be a/an
[A] intrinsic semiconductor
[B] p-type semiconductor
[C] n-type semiconductor
[D] p-n junction diode
Answer: p-n junction diode
(16) A strip of copper and another of germanium are cooled from room temperature to 80K. The resistance of
[A] each of these decreases
[B] copper strip increases and that of germanium decreases
[C] copper strip decreases and that of germanium increases
[D] each of these increases
Answer: copper strip decreases and that of germanium increases
(17) The diffusion 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: p-side to the n-side
(18) If the two ends of a p-n junction are joined by a wire
[A] there will not be a steady current in the circuit
[B] there will be a steady current from the n-side to the p side
[C] there will be a steady current from the p-side to the n side
[D] there may or may not be a current depending upon the resistance of the connecting wire
Answer: there will not be a steady current in the circuit
(19) Forward biasing is that in which applied voltage
[A] increases potential barrier
[B] cancels the potential barrier
[C] is equal to 1.5 volt
[D] None of these
Answer: cancels the potential barrier
(20) 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: there will be more free electrons than holes in the semiconductor

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