Based on the Electronic Devices, some of the important questions are covered in this question paper. The questions are prepared from the book back and the creative questions.

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Questions:

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 20. If the input signal is 0.01 volt, Calculate the output ac signal.

Find the number density of impurity atoms that must be added to a pure silicon crystal inorder to convert it to have resistivity
(i) \(10^{ -1 }\Omega m\ n\)-type silicon
(ii) \(10^{ -1 }\Omega m\ p\)-type silicon. Given for silicon:\(\mu _{ e }=0.135{ m }^{ 2 }V^{ -1 }\ s^{ -1 }\) and \(\mu _{ h }=0.048{ m }^{ 2 }V^{ -1 }\ s^{ -1 }\) .

How will you test in a simple way whether a transistor is spoiled or in working order?

Distinguish between electrons and holes.

Give any two difference between a half wave rectifier and a full wave rectifier.

Write the functions of three segments of a transistor.

Write two characteristic features to distinguish between n-type and p-type semiconductors.

A Zener of power rating 1 W is to be used as a voltage regulator. If Zener has a breakdown of 5 V and it has to regulate voltage which fluctuated between 3 V and 7 V, what should be the value of R_S for safe operations as shown below figure?

The conduction band in a solid is partially filled at 0 k. The solid sample is

(a)

Conductor

(b)

Semiconductor

(c)

Insulator

(d)

none of these

10.

A p-type semiconductor is obtained by doping silicon with

(a)

germanium

(b)

gallium

(c)

bismuth

(d)

Phosphorus

11.

Which type of semiconductor is obtained by mixing arsenic with silicon?

(a)

\(n-type\)

(b)

\(p-type\)

(c)

Both

(d)

None

12.

In a common-emitter configuration, a transistor \(\beta =50\) and input resistance \(1k\ \Omega \) if the peak value of a.c.input is 0.01 V then the peak value of collector currents is

(a)

\(0.01\mu A\)

(b)

\(0.25\mu A\)

(c)

\(100 \ \mu A\)

(d)

\(10 \ \mu A\)

13.

The Boolean expression \(P+\overset { -- }{ P } Q\) where p and Q are the inputs of the logic circuit, represents

(a)

AND gate

(b)

NAND gate

(c)

NOT gate

(d)

OR gate

14.

Which of the following is/are correct relations is Boolean algebra?

(a)

\(A.B+\overset { -- }{ AB } =((A.B)\overset { -- }{ A } .\overset { -- }{ B } \)

(b)

\(A.B+\overset { -- }{ AB } =(\overset { --- }{ A.B) } (\overset { -- }{ A } .\overset { -- }{ B } )\)

(c)

\(\overset { --------------- }{ A.B+(\overset { -- }{ A } .\overset { -- }{ B } ) } =\overset { --- }{ A.B } .(\overset { ----\\ ---- }{ A } +\overset { ----\\ ---- }{ B } )\)

(d)

\(\\ \overset { --------------- }{ A.B+(\overset { -- }{ A } .B) } =(A.B).(\overset { ----\\ ---- }{ A } +\overset { ----\\ ---- }{ B } )\)

15.

The decimal equivalent of the binary number \((11010.101)_{ 2 }\) is

(a)

17+9.625

(b)

15+9.625

(c)

26+0.625

(d)

24+0.625

16.

The lighting emitting diode(LED),

(a)

is made from the semiconducting compound gallium arsenide phosphide

(b)

emits light when forward biased

(c)

is made from one of the two basic semiconducting materials,silicon or germanium

(d)

emits light when reverse biased.

17.

In Boolean algebra if A = 1 and B = 0 then the value of \(A+\overset { --- }{ B } \) is

(a)

(b)

(c)

A+B

(d)

A.B

18.

In \(p-n \) junction, the physical distance from one side of the barrier to the other is known as the ................... barrier and the difference of potential from one side of the barrier to other side is known as ............. barrier

19.

In p-n junction \(p\)-side is known as .................. and \(n\) is known as ..............

20.

For a transistor,the ratio of change in base-emitter voltage to the resulting change in the base current at constant emitter voltage is called..............

21.

The output of an OR gate assumes 1 (in level) if.............. inputs assume 1 (in level).

22.

A pure semiconductor germanium or silicon,free of every impurity is called intrinsic semiconductor, At room temperature, a pure semiconductor has a very small number of current carriers (electrons and holes).Hence,its conductivity is low.
When the impurity atoms of valence five or three are doped in a pure semiconductor,we get respectively \(n-\) type or \(p-\) type extrinsic semiconductor.In case of a doped semiconductor.\({ n }_{ e }n_{ h }={ n }_{ i }^{ 2 };\)when \({ n }_{ e }\) and \(n_{ h }\) are the number density of electrons and holes respectively and \({ n }_{ i }\) is the number density of intrinsic charge carriers in a pure semiconductor. The conductivity of extrinsic semiconductor is much higher than that that of intrinsic semiconductor.
Read the above passage and answer the following question:
(i) Name two materials to be doped in pure semiconductor of silicon to get (a) \(p-\)type semiconductor (b) \(n-\)type semiconductor
(ii) What do you learn from the above study?

23.

Manoj wanted to do social work during vacations.He visited a remote village where there was no electricity. He made up his mind to help the villagers for getting the solar panels. For this he educated the villagers about techonology and uses of solar panels.he requested the villagers to Villagers agreed and applied for the solar panels. They got the same from government at reduced price. When the solar panels started working,the villagers were happy.
Read the passage and answer the following questions:
(i) What is solar panel?
(ii) What is the basic principle of working of a solar cell?
(iii) What are the basic values you assess in Manoj?

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Answers Key:

Voltage gain of the first amplifier, V₁ = 10
Voltage gain of the second amplifier, V₂ = 20
Input signal voltage, V_i = 0.01 V
Output AC signal voltage = V_o
The total voltage gain of a two-stage cascaded amplifier is given by the product of voltage gains of both the stages, i.e.,
V = V₁ x V₂
= 10 x 20 = 200
We have the relation:
\(V=\frac{V_{0}}{V_{1}}\)
V₀ = V x V_i
= 200 x 0.01 = 2 V
Therefore, the output AC signal of the given amplifier is 2 V.

(i) \(4.63\times 10^{ 20 }\ m^{ -3 }\),
(ii) \(1.3\times 10^{ 21 }\ m^{ -3 }\)
(i) \(\frac { 1 }{ \rho } =en_{ e } \ \mu _{ e } \ or \ n_{ e }=\frac { 1 }{ \rho e\mu _{ e } } \)
(ii) \(n_{ h }=\frac { 1 }{ \rho e\mu _{ h } } \)

A transistor has two junctions; one junction between emitter and base and other between base and collector. A junction of transistor has low resistance when forward biased and high resistance when reverse biased. In a spoiled transistor, the resistance of the junction is found to be low when forward biased or reverse biased, which can be checked using AVO-meter.

(i) Electron is a negatively charged particle having charge \(=1.6\times 10^{ -19 }C\) . Hole is a seat having positive charge which is produced when an electron breaks away from a covalent bond in a semiconductor. Hole is having the same charge as that of electron.
(ii) Energy of a hole is high as compared to that of electron.
(iii) The mobility of a hole is smaller than that of electron.

(i) In half wave rectifier, the output voltage is unidirection intermittent and varying voltage.
In full wave rectifier, the output voltage is unidirectional varying voltage.
(ii) In half wave rectifier, the frequency of output signal is same as that of input signal.
In full wave rectifier, the frequency of output signal is double than that of input signal.

The function of emitter is to emit the majority carriers. Function of collector is to collect the majority carriers coming from emitter through base. Base provides the proper interaction between the emitter and the collector.

(i) In n-type semiconductor, the semiconductor is doped with pentavalent impurity. The electrons are majority carriers and holes are minority carriers or n_e >> n_h, (n_e = number density of electrons, n_h = number density of holes).
In energy band diagram of n-type semiconductor, the donor energy level E_D is slightly below the bottom of conduction band E_c and thus. the electron can move to conduction band, even with small supply of energy.

(ii) In p-type semiconductor, the semiconductor is doped with trivalent impurity. The holes are the majority carriers and electrons are the minority carriers, i.e. n_b >> n_e . In energy band diagram of p-type, the acceptor energy level E_A is slightly above the top of valence band E_V .
Thus, even with small supply of energy, electron from valence band can jump to level E₄ and ionise the acceptor, negatively.

Give, power = 1 W, Zener breakdown, V_Z = 5 V
Minimum voltage, V_min = 3 V
Maximum voltage, V_max = 7 V
Current, \({ I }_{ Zmax }=\frac { P }{ { V }_{ Z } } =\frac { 1 }{ 5 } =0.2A\)
The values of R_S for safe operation,
\({ R }_{ S }=\frac { { V }_{ max }-{ V }_{ Z } }{ { I }_{ Zmax } } =\frac { 7-5 }{ 0.2 } =\frac { 2 }{ 0.2 } =10\Omega\)

Conductor

10.

(b)
gallium

11.

12.

(d)
\(10 \ \mu A\)

13.

(d)
OR gate

14.

(c)
\(\overset { --------------- }{ A.B+(\overset { -- }{ A } .\overset { -- }{ B } ) } =\overset { --- }{ A.B } .(\overset { ----\\ ---- }{ A } +\overset { ----\\ ---- }{ B } )\)

15.

(a)
17+9.625

16.

(a)
is made from the semiconducting compound gallium arsenide phosphide

17.

(a)
A

18.

()
Width of the: height of the capacitor

19.

()
anode ; cathode

20.

()
Input dynamic resistance of a transistors

21.

()
one or more

22.

(i) (a) The doping of pure silicon with boron or aluminium will give us \(p-\)type semiconductor
(b) The doping of pure silicon with arsenic or phosphorous will give us \(n-\)type semiconductor.
(ii) From the above study, we find that to get better output current ,pure semiconductor has to be adopted with suitable (impurity) atoms.Similarly,in day to day life,the appearence of right kind of persons(leaders) in society can improve their lot.

23.

(i) Solar panel is a panel having large number of solar cells fitted side by side on it.
(ii) Solar cell is basically a solar energy concerter.It is a \(p-n\)junction device which converts solar energy into electrical energy .If this energy is stored in a capacitor,it can be used for glowing bulbs.
(iii) Manoj displayed his will to do something for society.Trough his shear in a capacitor,it can be used for glowing bulbs.
(iii) Manoj displayed his will to do something for soceity.Through his shear efforts,he got electricity within the reach of villagers, who were suffering otherwise.?The work of Manoj was highly appreciated by villagers.