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

Questions
1 n 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

Answer:the positive terminal of the battery is connected to

p–side and the depletion region becomes thin

2 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

Answer:electric field is maximum

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3 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

Answer:both the depletion region and barrier height are reduced
4 Barrier potential of a P-N junction diode does not depend on
A doping density
B diode design
C temperature
D forward bias

Answer:diode design
5 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

Answer:more than d.c. value
6 The average value of output direct current in a full wave rectifier is
A I0/π
B I0/2
C π I0/2
D 2 I0/π

Answer:2 I0/π
7 The average value of output direct current in a half wave rectifier is
A I0/π
B I0/2
C π I0/2
D 2 I0/π

Answer:I0/π
8 Bridge type rectifier uses
A four diodes
B six diodes
C two diodes
D one diode

Answer:four diodes
9 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

Answer:10–4 : 1
10 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.

Answer:the P side is at higher electrical potential than N side.
11 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)

Answer:(eeV/kT – 1)
12 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

Answer:increases, decreases
13 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:both n and v will increase
14 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

Answer:increases
15 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.

Answer:they are costly
16 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

Answer:the valence band is completely filled and the conduction band is partially filled
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

Answer:n α T3/2
18 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

Answer:they are light
19 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

Answer:close to the conduction band of the host crystal
20 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

Answer:close to the valence band of the host crystal

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