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(a) m
(b) Reverse biasing, 0 A
(b) d
(c) Forward biasing, 5 mA (c) d
(d) Reverse biasing, 2 mA CBSE 2023
(d)d
2. During the formation of a p-n junction
7. In a
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(c) both the diffusion current and drift current remain (b) th
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CBSE 2023 Assertie
Direction
3. At a certain temperature in an intrinsic semiconductor, statements
the electrons and holes, concentration is labelledR
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dopant, hole concentration increases to (a) I
4.5x 102 m,Inthe doped semiconductor, the 1

concentration of electrons (n,) will be CBSE 2023

(b) 1
(a) 3x 10 m-3 (b) 5x 10 m-3
(c) 5x 10 m-3 (d) 6.75>x 108 m (c) I
(d) I
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8. Asse
The concentration of electron can be find by using elect
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dona
holes is 4×10 m.If the number density of
intrinsic carriers is 1.2× 10' m, the number density 9. Asse
of electrons in it is
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 392 Chapterwise CBSE Solved Papers : PHYSICS
D,
31. Draw the energy band diagram when intrinsic 22
w
semiconductor (Ge) is doped with impurity atoms of
antimony (Sb). Name the extrinsic semiconductor, so D2 22

obtained and majority charge carriers in it.

CBSE SQP 2020-21 12
6V
32. Draw energy band diagram of p and n type Delhi 2013C
semiconductors. Also, write two differences between p 41. Write two characteristics features to distinguish
and n type semiconductors. CBSE SQP 2020-21 between n-type and p-type semiconductors.
All India 2012
33. (i) Explain the formation of energy bands in
crystalline solids.
3 Marks Questions
(ii) Draw the energy band diagrams of (a) a metal and
(b)a semiconductor. 42. Explain the roles of diffusion current and drift current
in the formation of the depletion layer in ap -n
34. A student wvants to use two p-n junction diodes to junction diode. CBSE 2023
convert alternating current into direct current. Draw
the labelled circuit diagram she would use and explain 43. In a pure semiconductor crystal of Si, if antimony is
how it works ? CBSE 2018 added, then what type of extrinsic semiconductor is
obtained? Draw the energy band diagram of this
35. The V-I characteristic of asilicon diode is as shown in extrinsic semiconductor so formed. SQP 2021-22
the figure. Calculate the resistance of thediode at (i)I
= 15mA and (ii) V=-10V 44. With the help of a circuit iagram explain the working
(1 mA) of a p-n junction diode as a full-wave rectifier. Also draw
its input and output waveforms. CBSE 2022 (Term-l)
30
45. Explain the formation of potential barrier and
Silicon depletion region in a p-njunction diode. What is effect
20
15 of applying forward bias on the width of depletion
Delhi2020
10
region?
-10 V 0 0.51 !! 46. Draw the circuit diagram of a full wave rectifier and
0.7 0.8 V explain its working. Also, give the input and output
waveforms. Delhi 2019
1A
Foreign 2015
47. Draw the circuit diagram of a full wave rectifier.
36. Distinguish between 'intrinsic' and 'extrinsic'
semiconductors?
Explain its working principle. Show the input
AllIndia 2015 waveforms given to the diodes D, and D, and the
37. Explain,with the help of a circuit diagram, the corresponding output waveforms obtained at the load
connected to the circuit. All India 2019
working of a p-n junction diode as a half-wave rectifier.
AllIndia 2014 48. (i) In the following diagram, is the junction diode
38. Draw energy band diagram of n-type and p-type. forward biased or reverse biased?
semiconductor at temperature T> OK. Mark the donar
and acceptor energy level with their energies. +5 V

Foreign 2014
39. Distinguish between a metal and an (ii) Draw the circuit diagram of a full waye rectifier
basis of energy band diagram. insulator on the AllIndia 2017
Foreign 2014 and state how it works?
40. Assuming that the two diodes D, and D, used 49. Write the two processes that take place in the
in the formation of a p-n junction. Explain with the help ol a
electric circuit shown in the figure are ideal, find out
the value of the current flowing diagram, the formation of depletion region andDelhi
barrier
through 12 resistor. 2017
potential in a p-njunction.
394 Chapterwise CBSE Solved Papers : PHYSICS
+5V +10V 9
(a) in thc circuits (1) and (2)
(c) (d) (b) in thc circuits (2) and (3)
(c) in the circuits (1) and (3)
R
+5V oK W (d) only in the circuit (1)
(iv) I(mA)
30
(iüi) Based on the V-] characteristics of the diode, we
can classify diode as -Silicon
(a)bilateral device 20
(b)ohmic device
15
(c) non-ohmic device
(d) passive element 10

Or
Two identical p-n junctions can be connected in -10 V
series by three different methods as shown in the
1uA
0.5 V
(volt)
figure. If the potential difference in the junctions 0.7 0.8
is the same, then the correct connections will be
The V-I characteristic of a diode is shown in the
figure. The ratio of the resistance of the diode at
I=15 mA to the resistance at V=-10V is
(a) 100 (b) 106
(c) 10 (d) 10-6
(1) (2) (3)

Explanations
1. (c)Given, thresholdvoltage for p-njunctiondiode, Aswe know, n n, =n
V=0.7 V (n,)
Rp =100Q n
VD0.5 (1.5x 105)?
Current inp-n junction diode, Ip =5x10 m-3
100
Rp 4.5x 1022
Ip =5x]0-3 4. (c) Given that,
Ip =5 mA Number density of holes = 4 x 1020
The given diode is in forward biasing which having Number density of intrinsic =l.2x 10!5
current of 5 mA,
2. (d) During the formation of a p-n junction diffusion Then, number density of electrons, n = pxn
curTent remains almost constant but drift current where, p is the number density of holes and n is the
increases till both currents become equal. number density of electrons.
3. (b)Given, 4x10 xn= (1.2x 105)?
concentration of hole and electron
n, =1.5x 10'6 m-3 We get, n=
(1.2x 10!5y? =3.6x 10 m
4x 1020
n, = 1.5x 10l6 m-3
flows
n, =4.5x 1022 m3 5. (d) A pnjunction is a device in which current
through the junction when it is forward biased,
n =? whereas when reverse biased and conduct very sma1
 Semiconductor 389
Electronics
(iii)Reverse bias supports the resistance in forward bias
00000002
current flows across the potential barrier and no junction diode offer veryy low
reverse bias.
of the majority
carriers. junction due to the diffusion and very high
resistance in
The DC Transformer

, The
resistance of ajunction diode, pc = A
D

dynamic AV resistance or AC resistance of junction

S.
Output
diode, rAC =

Diode as a Rectifier
o0000000
D
D
The process of converting 0900000090
alternating voltage/current into
direct voltage/current is called A
as a rectifier for
converting
rectification. Diode is used
alternating
direct current/voltage. There are two current/voltage into
as a rectifier. ways of using a diode RL

S: B
(i) Diode as a Half-Wave Rectifier
Diode conducts corresponding to positive half cycle and Circuit diagrom of full-wave rectifier
does not conduct during negative half cycle. Hence, AC is
converted by diode into unidirectional pulsating DC. This A waveforms have been given below
The input and output
at
action is known as half-wave rectification. Waveform
Transformer
p-n (a
B
P
at
utput Waveform
.RL
Output
waveform
R) Due tojDue to Due to Due to
(across
B D D1, D2
Circuit diagram for Diode as o half-wave rectifier

output waveforms have been given below

The input and A,
at (a)
Voltage
Input AC (i) The average value or DCvalue obtained from a
half-wave rectifier,
R, Ipc =
across
(ii) The average value or DC value obtained from a
Voltage Output voltage full-wave rectifier,
fo 2/0
t
(b) (iii) The pulse frequency of a half-wave rectifier is
Input and outpUt waveforms tofrequency of AC. equal
(iv) The pulse frequency of a full-wave
(ü) Diode as a Full-Wave Rectifier to that of AC. rectifier is double
junction diodes, D, and
In the full-wave rectifier, two p-n the principle that
Oz are used. Its working is based on