Question Pool Semiconductor Electronics: Materials, Devices and Simple Circuits

# Semiconductor Electronics: Materials, Devices and Simple Circuits - SAMAGRA Question Pool & Answers | Class 12

Kerala Syllabus SAMAGRA SCERT SAMAGRA Question Pool for Class 12 Physics Semiconductor Electronics: Materials, Devices and Simple Circuits

Qn 1.

The current amplification factor for CB configuration of a transistor is 0.9. Find out the current amplification factor for CE configuration.

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Qn 2.

The symbol of a diode is shown in the figure

a) The diode is a ................................(rectifier diode/ photo diode/ zener diode )

b) Draw V – I characteristic of the above diode

c) A zener diode with Vz = 6 V is used for voltage regulation. The current through the load is to be 4 mA and that through the zener diode is 20 mA. If the unregulated input is 10 V, what is the value of series resistor R?

d) What is the fundamental frequency of the ripple in a full wave rectifier circuit operating from 50 Hz mains?

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Qn 3.

Draw the symbol of NAND Gate.

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Qn 4.

(A) What do you mean by barrier potential of a diode?

(B) With the help of a diagram explain the working of a full wave rectifier.

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Qn 5.

(a) Which of the following symbol represents a universal gate?

(b) Shown below is an experimental set up with a semiconductor diode

(i) identify the experiment

(ii) draw the resulting graph

(c) with the help of a neat circuit diagram obtain an expression for voltage gain of a transistor amplifier in C-E configuration.

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Qn 6.

A logic circuit is shown in the figure:

Complete the truth table of the circuit. Name the resulting gate formed by the combination of the above gates.

0 1 0 1

1 0 0 1

1 1 0

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Qn 7.

A graph showing the variation of current (I) flowing through a p-n junction with the

voltage (V) applied across it is called the V-I characteristics of a p-n junction.

(a) V-I characteristic of a forward biased diode is shown in the figure.

Write any two important features of the graph.

(b) What is a Zener diode? Give its symbol.

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Qn 8.

How will the readings of ammeter and voltmeter change , if the value of resistance R1 is increased?

As R1 increases input current decreases and hence collector current decreases. As a result voltage across R2

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Qn 9.

A  full wave rectifier circuit is shown in figure

(a) Draw the output wave form of the rectifier

(b) If a full wave rectifier circuit is operating from 50 Hz mains, the fundamental frequency in the ripple will be

(a) 50 Hz (b) 70.7 Hz (c) 100 Hz (d) 25 Hz

(c)In a zener regulated power supply, a zener diode with Vz = 6.0 V is used for regulation. The load current is to be 4.0 mA and the unregulated input 10.0 V. What is the value of series resistor R?

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Qn 10.

Diods are one of the building elements of electronic circuits. Some type of diods are shown in the figure.

(i)

(ii)

(iii)

(a)Identify rectifier diode from the figure.

(b)Draw the circuit diagram of a forward biased rectifier diode by using a battery

(c)Draw the forward and reverse bias characteristics of a rectifier diode and mark thresh hold voltage or cut in voltage .

(d) What happens to the resistance of a semiconductor on heating?

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Qn 11.

The following diagram shows energy bands in a semiconductor

(a) which diagram shows energy band positions at 0K

(b) What do you mean by energy gap?.Match the elements /compounds with their respective energy gap values.

(c)Classifiy solids into conductors , semiconductors, and insulators by drawing energy diagram

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Qn 12.

Forward biased pn junction diodes are shown in the figure

(a) Identify the figure, which shows the correct direction of flow charges

(b) What do you mean by barrier potential and depletion region of a pn junction?

(c)When forward bias is applied to a p-n junction, what happens to the potential barrier and the width of depletion region.

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Qn 13.

The basic building blocks of digital electronic circuits are called Logic Gates. Some logic gates and their names are given in the table

Match the symbols of logic gates with their names.

(b)Draw the output wave form, from the given input waveform of a NAND gate as shown in figure(input terminals are A and B).

(c) Write the truth table for the given circuit

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Qn 14.

The transfer characteristic of n-p-n transistor in CE configuration is shown in the figure

(a)Identify the cut-off region, active region, saturation region from the figure

(b )In which of these regions, a transistor is said to be switched off

(c) For a CE transistor amplifier, the audio signal voltage across collector resistance of 2.0 kΩ is 2.0 V. Suppose the current amplification factor of the transistor is 100. What should be the value of Rin series with VBB supply of 2.0V, if DC base current has to be 10 times the signal current?

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

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Qn 15.

LEDs that can emit red, yellow, orange,etc commercially available.

(a)How these colours are obtained in a LED

(b)Write any two uses of LED

(c) What are its advantages over ordinary bulbs ?

(a)Different colours are obtained by changing the concentration of arsenic and phosphors in Gallium Arsenide

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Qn 16.

E1,E2 and E3 are the forbidden energy band gap in semiconductors, conductors, and insulators.

(a)What do you mean by forbidden energy band gap

(b)Arrange E1,E2 and E3 ascending order.

(c) Arrange the energy band gap of carbon, silicon and germanium in ascending order.

(a)The gap between the top of the valence band and bottom of the conduction band is called the energy band gap.

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Qn 17.

A typical illuminated p-n junction solar cell is shown in figure.

(a)In which direction photo current flows through the load resistor.

(b)What are the basic process for the generation of emf by a solar cell?

(c)Draw the I-V characteristics of a solar cell.

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Qn 18.

An illuminated photodiode is shown in figure.

(a)Identify the nature of biasing of the diode

(b)Draw the I-V characteristics of a photodiode.

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Qn 19.

There are semiconductor devices in which charge carriers are generated by photons.

(a)What is the name of such devices?

(b)Give two examples for such devices.

(a)Optoelectronic devices.

(b)Photodiode,light emitting diode, solar cells

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Qn 20.

Zener diode is fabricated by heavily doping both p-, and n- sides of the junction of a diode.

(a)Draw the symbol of a zener diode

(b) which property of the zener diode is used for regulating supply voltages

(c)What do you mean by internal field emission

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Qn 21.

The symbol of a special purpose semiconductor diode is shown in figure.

(a)Identify the symbol

(b)draw its I-V characteristics

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Qn 22.

Filter circuits are used in a rectifier to get steady dc output from the pulsating voltage

(a)Draw a fullwave rectifier with a capacitor filter

(b)Draw its input and output wave form of voltage

(c)In filter circuits inductors are used in ---------- (series/parallel)with the resistor.

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Qn 23.

A pn junction formation is shown in the figure.

Redraw the figure and indicate the direction of electron drift, hole drift, electron diffusion, and hole diffusion.

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Qn 24.

Give logic circuit of an OR gate using NAND gates only.

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Qn 25.

What is the expression for the frequency of oscillations produced by a tank circuit.

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Qn 26.

When both the inputs are high what is the output of NAND gate?

Zero.

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Qn 27.

In the circuits shown, the switch which is open represents the logic state 0 and the switch which

in closed represents the logic state 1. The lamp is lit when output is logic state 1. What type of

gates are represented by the circuits in (i) and (ii)?

Circuit (i) represents an AND gate and circuit (ii) represents an OR

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Qn 28.

Define a.c. current gain βac for common-emitter configuration.

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Qn 29.

Why is the emitter of a transistor forward biased and the collector reverse biased?

The forward biased emitter sends the majority carriers into the base regions and the reverse biased collector pulls these majority

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Qn 30.

draw the circuit of a common-emitter amplifier

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Qn 31.

Why is a common-emitter amplifier generally preferred over a common base amplifier?

The current gain of a common-emitter amplifier is much more than that of a common-base amplifier. Therefore the voltage amplification is

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Qn 32.

In a transistor, base is made thin and is doped very lightly. Why?

Base is made very thin and is doped lightly so that most of the carriers are attracted straight into the collector and very few combine

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Qn 33.

State how the thickness of the depletion region will change when the pn junction diode is

(i) forward biased

(ii) reversed biased.

the thickness of the depletion region decreases when the junction diode is forward baised and increases when the diode is reverse

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Qn 34.

How does the mobility of carriers in a semiconductor vary with temperature?

Mobility of carriers decreases slightly with rise in

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Qn 35.

Which process causes depletion region in a pn junction

Diffusion of electrons and holes across the junction, and their consequent recombination, causes

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Qn 36.

Which type of impurity should be added to Ge to have a p-type and n-type semiconductor?

Holeand

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Qn 37.

a. What are the energy gaps for Ge and Si?

b. What is the value of forbidden energy gap for a conductor?

c. What are p-type and n-type   semiconductors?

a) Ge : 0.7 eV; Si : 1.1 eV.

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Qn 38.

Semiconductors are one of  the building blocks of  electronic devices

a. What happens to the resistance of a semiconductor on heating?

b. What are the charge carriers in semiconductors?

c. Distingusih between intrinsic and extrinsic semiconductors?

a. The resistance of a semiconductor decreases with rise in temperature.

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Qn 39.

A digital circuit is constructed using three gates as shown.

(a)Identify the gates p and q

(b)write the truth table for the given circuit

(c)Why NAND gate is known as universal gate?

(a)p-not gate,q-nor gate

(b)