Physics MCQs for Class 12 Semiconductor Electronics
Q.1. 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 free electrons is more than that in a conductor
Q.2. Let nh and ne be the number of holes and conduction electrons in an extrinsic
semiconductor. Then
(a) nh > ne (b) nh = ne (c) nh < ne (d) nh ≠ ne
Q.3. A p-type semiconductor is
(a) positively charged
(b) negatively charged
(c) uncharged
(d) uncharged at 0K but charged at higher temperatures
Q.4. 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
Q.5. The impurity atoms with which pure silicon may be doped to make it a p-type
semiconductor are those of
(a) phosphorus (b) boron (c) antimony (d) nitrogen
Q.6. 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
Q.7. The resistivity of a semiconductor at room temperature is in between
(a) 10–2 to 10–5 Ω cm (b) 10–3 to 106 Ω cm (c) 106 to 108 Ω cm (d) 1010 to 1012 Ω cm
Q.8. Number of electrons in the valence shell of a pure semiconductor is
(a) 1 (b) 2 (c) 3 (d) 4
Q.9. In a semiconductor, the forbidden energy gap between the valence band and the
conduction band is of the order is
(a) 1 MeV (b) 0.1 Mev (c) 1 eV (d) 5 eV
Q.10. The forbidden energy gap for germanium crystal at 0 K is
(a) 0.071 eV (b) 0.71 eV (c) 2.57 eV (d) 6.57 eV
Q.11. In an insulator, the forbidden energy gap between the valence band and
conduction band is of the order of
(a) 1 MeV (b) 0.1 MeV (c) 1 eV (d) 5 eV
Q.12. What is the resistivity of a pure semiconductor at absolute zero ?
(a) Zero
(b) Infinity
(c) Same as that of conductors at room temperature
(d) Same as that of insulators at room temperature
Q.13. Temperature coefficient of resistance of semiconductor is
(a) zero (b) constant (c) positive (d) negative
Q.14. In a p-type semiconductor, the acceptor valence band is
(a) close to the valence band of the host crystal
(b) close to conduction band of the host crystal
(c) below the conduction band of the host crystal
(d) above the conduction band of the host crystal
Q.15. In an n-type semiconductor, donor valence band is
(a) above the conduction band of the host crystal
(b) close to the valence band of the host crystal
(c) close to the conduction band of the host crystal
(d) below the valence band of the host crystal
Q.16. The mobility of free electrons is greater than that of free holes because
(a) they are light
(b) they carry negative charge
(c) they mutually collide less
(d) they require low energy to continue their motion
Q.17. The relation between number of free electrons (n) in a
semiconductor and temperature (T) is given by
(a) n α T (b) n α T2 (c) n α √T (d) n α T3/2
Q.18. In semiconductors, at room temperature
(a) the conduction band is completely empty
(b) the valence band is partially empty and the conduction band is partially filled
(c) the valence band is completely filled and the conduction band is partially filled
(d) the valence band is completely filled
Q.19. At absolute zero, Si acts as
(a) non-metal (b) metal (c) insulator (d) None of these
Q.20. One serious drawback of semi-conductor devices is
(a) they do not last for long time.
(b) they are costly
(c) they cannot be used with high voltage.
(d) they pollute the environment.
Q.21. When an impurity is doped into an intrinsic semiconductor,
the conductivity of the semiconductor
(a) increases (b) decreases
(c) remains the same (d) becomes zero
Q.22. 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
Q.23. 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
Q.24. By increasing the temperature, the specific resistance of a
conductor and a semiconductor
(a) increases for both (b) decreases for both
(c) increases, decreases (d) decreases, increases
Q.25. 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
Q.26. Carbon, Silicon and Germanium atoms have four valence electrons each.
Their valence and conduction bands are separated by energy band gaps represented
by (Eg)C, (Eg)Si and (Eg)Ge respectively. Which one of the following relationship is
true in their case?
(a) (Eg)C > (Eg)Si (b) (Eg)C < (Eg)Si (c) (Eg)C = (Eg)Si (d) (Eg)C < (Eg)Ge
Q.27. 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
Q.28. 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
Q.29. 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
Q.30. 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
Q.31. 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
Q.32. 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
Q.33. 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
Q.34. In reverse biasing
(a) large amount of current flows
(b) potential barrier across junction increases
(c) depletion layer resistance increases
(d) no current flows
Q.35. Zener diode is used for
(a) amplification (b) rectification (c) stabilisation (d) all of the above
Q.36. Filter circuit
(a) eliminates a.c. component
(b) eliminates d.c. component
(c) does not eliminate a.c. component
(d) None of these
Q.37. For a junction diode the ratio of forward current (If) and
reverse current (Ir) is
[e = electronic charge,
V = voltage applied across junction,
k = Boltzmann constant,
T = temperature in kelvin]
(a) e–V/kT (b) eV/kT
(c) (e–eV/kT + 1) (d) (eeV/kT – 1)
Q.38. 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
Q.39. In a P -N junction
(a) the potential of P & N sides becomes higher alternately
(b) the P side is at higher electrical potential than N side.
(c) the N side is at higher electric potential than P side.
(d) both P & N sides are at same potential.
Q.40. Barrier potential of a P-N junction diode does not depend on
(a) doping density (b) diode design
(c) temperature (d) forward bias
Q.41. 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
Q.42. In forward biasing of the p–n junction
(a) the positive terminal of the battery is connected to
p–side and the depletion region becomes thick
(b) the positive terminal of the battery is connected to
n–side and the depletion region becomes thin
(c) the positive terminal of the battery is connected to
n–side and the depletion region becomes thick
(d) the positive terminal of the battery is connected to
p–side and the depletion region becomes thin
Q.43. When p-n junction diode is forward biased then
(a) both the depletion region and barrier height are reduced
(b) the depletion region is widened and barrier height is
reduced
(c) the depletion region is reduced and barrier height is
increased
(d) Both the depletion region and barrier height are increased
Q.44. The cause of the potential barrier in a p-n junction diode is
(a) depletion of positive charges near the junction
(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
Q.45. The ratio of forward biased to reverse biased resistance
for p-n junction diode is
(a) 10–1 : 1 (b) 10–2 : 1 (c) 104 : 1 (d) 10–4 : 1
Q.46. 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 is zero
Q.47. Bridge type rectifier uses
(a) four diodes (b) six diodes (c) two diodes (d) one diode
Q.48. The average value of output direct current in a half wave rectifier is
Q.49. The average value of output direct current in a full wave rectifier is
Q.50. In a half wave rectifier, the r.m.s. value of the a.c. component of the wave is
(a) equal to d.c. value (b) more than d.c. value
(c) less than d.c. value (d) zero
