NCERT Solutions Class 12 Physics Chapter 14 Semiconductor Electronics: Materials, Devices And Simple Circuits Download In Pdf

Chapter 14 Semiconductor Electronics: Materials, Devices and Simple Circuits Download in pdf

**Question 14.1** In an n-type silicon, which of the following statement is true:

(a) Electrons are majority carriers and trivalent atoms are the
dopants.

(b) Electrons are minority carriers and pentavalent atoms are the
dopants.

(c) Holes are minority carriers and pentavalent atoms are the
dopants.

(d) Holes are majority carriers and trivalent atoms are the dopants.

**Question 14.2** Which of the statements given in Exercise 14.1 is true for p-type
semiconductos.

**Question 14.3** Carbon, silicon and germanium have four valence electrons each.
These are characterised by valence and conduction bands separated
by energy band gap respectively equal to (Eg)C, (Eg)Si and (Eg)Ge. Which
of the following statements is true?

(a) (Eg)Si < (Eg)Ge < (Eg)C
(b) (Eg)C < (Eg)Ge > (Eg)Si
(c) (Eg)C > (Eg)Si > (Eg)Ge
(d) (Eg)C = (Eg)Si = (Eg)Ge

**Question 14.4 **In an unbiased p-n junction, holes diffuse from the p-region to
n-region because

(a) free electrons in the n-region attract them.

(b) they move across the junction by the potential difference
.

(c) hole concentration in p-region is more as compared to n-region.

(d) All the above.

**Question 14.5** When a forward bias is applied to a p-n junction, it
(a) raises the potential barrier.

(b) reduces the majority carrier current to zero.

(c) lowers the potential barrier.

(d) None of the above.

**Question 14.6** For transistor action, which of the following statements are correct:

(a) Base, emitter and collector regions should have similar size and
doping concentrations.

(b) The base region must be very thin and lightly doped.

(c) The emitter junction is forward biased and collector junction is
reverse biased.

(d) Both the emitter junction as well as the collector junction are
forward biased.

**Question 14.7** For a transistor amplifier, the voltage gain
(a) remains constant for all frequencies.

(b) is high at high and low frequencies and constant in the middle
frequency range.

(c) is low at high and low frequencies and constant at mid
frequencies.

(d) None of the above.

**Question 14.8** In half-wave rectification, what is the output frequency if the input
frequency is 50 Hz. What is the output frequency of a full-wave rectifier
for the same input frequency.

**Question 14.9** For a CE-transistor amplifier, the audio signal voltage across the
collected resistance of 2 kΩ is 2 V. Suppose the current amplification
factor of the transistor is 100, find the input signal voltage and base
current, if the base resistance is 1 kΩ.

**Question 14.10** Two amplifiers are connected one after the other in series (cascaded).
The first amplifier has a voltage gain of 10 and the second has a
voltage gain of 20. If the input signal is 0.01 volt, calculate the output
ac signal.

**Question 14.11** A p-n photodiode is fabricated from a semiconductor with band gap
of 2.8 eV. Can it detect a wavelength of 6000 nm?

ADDITIONAL EXERCISES QUESTIONS

**Question 14.12** The number of silicon atoms per m3 is 5 × 1028. This is doped
simultaneously with 5 × 1022 atoms per m3 of Arsenic and 5 × 1020
per m3 atoms of Indium. Calculate the number of electrons and holes.
Given that ni = 1.5 × 1016 m–3. Is the material n-type or p-type?

**Question 14.13** In an intrinsic semiconductor the energy gap Eg is 1.2eV. Its hole
mobility is much smaller than electron mobility and independent of
temperature. What is the ratio between conductivity at 600K and
that at 300K? Assume that the temperature dependence of intrinsic
carrier concentration ni is given by
0 exp –
2
g
i
B
E
n n
k T
=
where n0 is a constant.

**Question 14.14 **In a p-n junction diode, the current I can be expressed as
0 exp – 1
2 B
eV
I I
k T
where I0 is called the reverse saturation current, V is the voltage
across the diode and is positive for forward bias and negative for
reverse bias, and I is the current through the diode, kB is the
Boltzmann constant (8.6×10–5 eV/K) and T is the absolute
temperature. If for a given diode I0 = 5 × 10–12 A and T = 300 K, then
(a) What will be the forward current at a forward voltage of 0.6 V?

(b) What will be the increase in the current if the voltage across the
diode is increased to 0.7 V?

(c) What is the dynamic resistance?

(d) What will be the current if reverse bias voltage changes from 1 V
to 2 V?

**Question 14.15** You are given the two circuits as shown in Fig.14.44. Show that
circuit (a) acts as OR gate while the circuit (b) acts as AND gate.

**Question 14.16** Write the truth table for a NAND gate connected as given in
Fig. 14.45.Hence identify the exact logic operation carried out by this circuit.

**Question 14.17** You are given two circuits as shown in Fig. 14.46, which consist
of NAND gates. Identify the logic operation carried out by the two
circuits.

**Question 14.18** Write the truth table for circuit given in Fig. 14**.**47 below consisting
of NOR gates and identify the logic operation (OR, AND, NOT) which
this circuit is performing. (Hint: A = 0, B = 1 then A and B inputs of second NOR gate will be 0
and hence Y=1. Similarly work out the values of Y for other
combinations of A and B. Compare with the truth table of OR, AND,
NOT gates and find the correct one.)

**Question 14.19** Write the truth table for the circuits given in Fig.
14.48 consisting of
NOR gates only. Identify the logic operations (OR, AND, NOT) performed
by the two circuits.

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- Chapter 1 Electric Charges and Fields
- Chapter 2 Electrostatic Potential and Capacitance
- Chapter 3 Current Electricity
- Chapter 4 Moving Charges and Magnetism
- Chapter 5 Magnetism and Matter
- Chapter 6 Electromagnetic Induction
- Chapter 7 Alternating Current
- Chapter 8 Electromagnetic Waves
- Chapter 9 Ray Optics and Optical Instruments
- Chapter 10 Wave Optics
- Chapter 11 Dual Nature of Radiation and Matter
- Chapter 12 Atoms
- Chapter 13 Nuclei
- Chapter 14 Semiconductor Electronics: Materials, Devices and Simple Circuits
- Chapter 15 Communication Systems

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