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CBSE 12th Standard Physics Subject Semiconductor Electronics Materials Devices And Simple Circuits HOT Questions 2 Mark Questions 2021

Published on: 27/05/2021

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Std: 12th Standard CBSE - Physics

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Questions:

Generic 2

5 x 2 = 10

Give a brief explanation that how a NOT gate is realised Using NAND gate.

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?

Two car generates have a common gate which needs to open automatically when a car enters either of the garages or cars enter both. A circuit, that resembles this situation using diodes for this situation.

In normal case, emitter-base junction is the forward bias and collector-base junction is reverse biased. What will happen if emitter is reverse biased and collector is forward biased?

In the working of a transistor, emitter-base junction is forward biased while collector-base junction is reverse biased. Why?

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Answers Key:

Generic 2

5 x 2 = 10

If the inputs of NAND gate are joined together, then the NAND gate functions as NOT gate. Thus,

Truth Table

A	A=B	Y
0	0	1
1	1	0

\(Y=\bar { A.A } =\bar { B.B } =\bar { A } =\bar { B } \)

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,
\({ R }_{ S }=\frac { { V }_{ max }-{ V }_{ Z } }{ { I }_{ Zmax } } =\frac { 7-5 }{ 0.2 } =\frac { 2 }{ 0.2 } =10\Omega\)

As, car enters in the gate, any one or both are opened. The device is shown below:

So, OR gate gives the desired output

A	B	C
0	0	0
0	1	1
1	0	1
1	1	1

If emitter is reverse biased and collector is forward biased, then emitter works as collector and collector is work as emitter. In such situation, transistor works but has lower amplification because the size of emitter is smaller than collector and doping of emitter is more than collector.

The emitter will send the majority carriers (electrons or holes) towards base only, when it is forward biased. The collector will collect the majority carriers only when it is reversed biased.