33 Years NEET-AIPMT Chapterwise Solutions - Physics 2020

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Semiconductor Electronics : Materials, Devices and Simple Circuits
139
\ Wavelength of light emitted,
1242 eV-nm
λ= = 654 nm
19 . eV
53. (a) : The V-I characteristic for a solar cell is as
shown in the figure.
54. (a) :
Here, Y = A+ B = AB ⋅ = AB ⋅
This AND Gate. So, the truth table is
A B Y
0 0 0
0 1 0
1 0 0
1 1 1
60. (d) : LED bulb will light up if switch(s) A or B or
both A and B is/are open. Hence it represents a NAND
gate.
61. (b) :
The voltage drop across 1 kW = V Z = 15 V
The current through 1 kW is
15 V
−3
I′ = = 15 × 10 A=
15 mA
1 ×
3
10 Ω
The voltage drop across 250 W = 20 V – 15 V
= 5V
The current through 250 W is
5 V
I = = 002A=
20 mA
250 Ω .
The current through the zener diode is
I Z = I – I′ = (20 – 15)mA = 5 mA
55. (c) : Band gap = 2.5 eV
The wavelength corresponding to 2.5 eV
12400 eV Å
= = 4960Å.
2.5 eV
4000 Å can excite this.
56. (d) : Band gap = 2 eV.
Wavelength of radiation corresponding to this energy,
hc 12400 eVÅ
λ= = = 6200Å
E 2 eV
The frequency of this radiation
8
c 3×
10 m/s
= =
λ 6200 × 10
− ⇒ u = 5 × 10
10
14 Hz.
m/s
57. (c) : Zener diode is used for stabilisation while p-n
junction diode is used for rectification.
58. (b) : In photocell, photoelectromotive force,
is the force that stimulates the emission of an electric
current when photovoltaic action creates a potential
difference between two points and the electric current
depends on the intensity of incident light.
59. (a) : A A
B
B
Y
62. (b) :
Y = ( A⋅ B+ A⋅B)
At output, the truth table corresponds to NOR gate.
63. (c) :
Y = ( ABC ) = ABC
If A= B= C= 0then
Y0
= 0=
1
If A= B= C= 0then
Y1
= 1=
0
64. (b) :
Output of the circuit, Y = (A + B)·C
Y = 1 if C = 1 and A = 0, B = 1
or A = 1, B = 0 or A = B = 1
65. (a) :
The output of the given logic circuit is
66. (a) :
X = AB . = AB .
The output of the given logic gate is
C= A⋅ B= A⋅B
It is the Boolean expression of AND gate.
Hence, the resulting gate is a AND gate.
67. (a) : The truth table of the given waveform is as
shown in the table.