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Semiconductor Electronics · Question 58

AIPMT 2012 (Prelims)MCQEasy📈 Topic in 0% papers+4−1
1

C and Si both have same lattice structure; having 4 bonding electrons in each. However, C is insulator whereas Si is intrinsic semiconductor. This is because

  1. In case of C the valence band is not completely filled at absolute zero temperature.
  2. In case of C the conduction band is partly filled even at absolute zero temperature.
  3. The four bonding electrons in the case of C lie in the second orbit, whereas in the case of Si they lie in the third.
  4. The four bonding electrons in the case of C lie in the third orbit, whereas for Si they lie in the fourth orbit.

Answer

(3) The four bonding electrons in the case of C lie in the second orbit, whereas in the case of Si they lie in the third.

Solution

The valence electrons of C (2s² 2p²) lie in the second orbit, while those of Si (3s² 3p²) lie in the third orbit.

Electrons in the second orbit are held much more tightly, so the energy gap of C (diamond) is large (Eg 5.4 eV) insulator.

For Si the valence electrons are in the third orbit, less tightly bound, and Eg 1.1 eV semiconductor.

As per NCERT, C (diamond), Si and Ge have the same lattice structure, and their difference in behaviour arises because the four bonding electrons lie in the second, third and fourth orbit respectively.

Answer: (3)

AIPMT 2012 (Prelims)

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2

The figure shows a logic circuit with two inputs A and B and the output C. The voltage wave forms across A, B and C are as given. The logic circuit gate is [figure]

  1. OR gate
  2. NOR gate
  3. AND gate
  4. NAND gate
AIPMT 2012 (Prelims)
3

In a CE transistor amplifier, the audio signal voltage across the collector resistance of 2 k is 2 V. If the base resistance is 1 k and the current amplification of the transistor is 100, the input signal voltage is

  1. 0.1 V
  2. 1.0 V
  3. 1 mV
  4. 10 mV
Out of syllabusAIPMT 2012 (Prelims)
4

Transfer characteristics [output voltage (V0) vs input voltage (Vi)] for a base biased transistor in CE configuration is as shown in the figure. For using transistor as a switch, it is used [figure]

  1. in region III
  2. both in region (I) and (III)
  3. in region II
  4. in region I
Out of syllabusAIPMT 2012 (Prelims)
5

A Zener diode, having breakdown voltage equal to 15 V, is used in a voltage regulator circuit shown in figure. The current through the diode is [figure]

  1. 5 mA
  2. 10 mA
  3. 15 mA
  4. 20 mA
AIPMT 2011 (Mains)
6

In the following figure, the diodes which are forward biased, are [figure]

  1. (A), (B) and (D)
  2. (C) only
  3. (C) and (A)
  4. (B) and (D)
AIPMT 2011 (Mains)
7

Pure Si at 500 K has equal number of electron (ne) and hole (nh) concentrations of 1.5 1016 m-3. Doping by indium increases nh to 4.5 1022 m-3. The doped semiconductor is of

  1. p-type having electron concentration ne = 5 109 m-3
  2. n-type with electron concentration ne = 5 1022 m-3
  3. p-type with electron concentration ne = 2.5 1010 m-3
  4. n-type with electron concentration ne = 2.5 1023 m-3
AIPMT 2011 (Mains)
8

In forward biasing of the p-n junction

  1. the positive terminal of the battery is connected to p-side and the depletion region becomes thick.
  2. the positive terminal of the battery is connected to n-side and the depletion region becomes thin.
  3. the positive terminal of the battery is connected to n-side and the depletion region becomes thick.
  4. the positive terminal of the battery is connected to p-side and the depletion region becomes thin.
AIPMT 2011 (Prelims)
9

Symbolic representations of four logic gates are shown as [figure] Pick out which ones are for AND, NAND and NOT gates, respectively

  1. (ii), (iii) and (iv)
  2. (iii), (ii) and (i)
  3. (iii), (ii) and (iv)
  4. (iii), (iv) and (ii)
AIPMT 2011 (Prelims)
10

If a small amount of antimony is added to germanium crystal

  1. it becomes a p-type semiconductor
  2. the antimony becomes an acceptor atom
  3. there will be more free electrons than holes in the semiconductor
  4. its resistance is increased
AIPMT 2011 (Prelims)
11

A transistor is operated in common emitter configuration at VC = 2 V such that a change in the base current from 100 A to 300 A produces a change in the collector current from 10 mA to 20 mA. The current gain is

  1. 50
  2. 75
  3. 100
  4. 25
Out of syllabusAIPMT 2011 (Prelims)

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