Download Important Questions for Class 12 Chapter 14 FREE PDF
Semiconductor Electronics, Chapter 14 of Class 12 Physics, introduces the fascinating world of semiconductors, their properties, and applications. This chapter's important questions cover key concepts like diodes, transistors, and logic gates, forming the foundation of modern electronics. It emphasises practical applications in circuits and devices. Download the Class 12 Physics Syllabus for detailed coverage and explore our exclusive Class 12 Physics Important Questions PDF to solidify your understanding and crack your exams.








Access Class 12 Physics Chapter 14: Semiconductor Electronic Material Devices and Simple Circuits Important Questions
1 Mark Questions
1. Give the ratio of number of holes and the number of conduction electrons in an intrinsic semiconductor.
Ans:
2. What type of impurity is added to obtain n-type semiconductor?
Ans: Pentavalent atoms (group -
3. Doping of silicon with indium leads to which type of semiconductor?
Ans: Doping of Silicon with Indium produces a p-type semiconductor as Indium is a trivalent impurity.
4. Draw an energy level diagram for an intrinsic semiconductor.
Ans:
In intrinsic semiconductor,
The energy level diagram for an intrinsic semiconductor is shown below:

5. A semiconductor has equal electron and hole concentration of
Ans:
According to the question, after doping,
Clearly, we get an n-type semiconductor after doping.
6. How does the energy gap of an intrinsic semiconductor vary, when doped with a trivalent impurity?
Ans: An acceptor energy level is formed in the forbidden energy gap above the valence band when an intrinsic semiconductor is doped with a trivalent impurity.
Due to this, electrons quickly jump to the acceptor energy level.
7. How does the width of the depletion layer of p-n-junction diode change with decrease in reverse bias?
Ans: The width of the depletion layer will decrease with decrease in reverse bias.
8. Under what condition does a junction diode work as an open switch?
Ans: A junction diode works as an open switch when it is connected under reverse bias conditions.
9. Which type of biasing gives a semiconductor diode very high resistance?
Ans: Reverse biasing gives a semiconductor diode very high resistance.
10. If the output of a 2-input NAND gate is fed as the input to a NOT gate,
a) name the new logic gate obtained and
Ans:
An AND gate is obtained when the output of a 2-input NAND gate is fed as the input to a NOT gate.
b) write down its truth table
Ans:
Truth table for an AND gate is given below.
A | B | Y |
0 | 0 | 0 |
0 | 1 | 0 |
1 | 0 | 0 |
1 | 1 | 1 |
11. Define current amplification factor in a common – emitter mode of transistor.
Ans: Current amplification factor is the fraction of a small change in collector current to the slight difference in base current at constant collector-emitter junction voltage.
12. Why is a semiconductor damaged by a strong current?
Ans: When a strong current traverses through a semiconductor, a large amount of heat is generated, which breaks the covalent links in the semiconductor. This causes the semiconductor to get damaged.
2 Marks Questions
1. Draw a p-n junction with reverse bias. Which biasing will make the resistance of a p-n-junction high?
Ans: The diagram of a p-n junction with reverse bias is as follows:

Reverse biasing will provide a high resistance and thus, will not permit the current to pass through the junction.
2. Write the truth table for the following combination of gates.

Ans:
Truth table for the given combination of gates is as follows:
A | B | Y’ | Y |
0 | 0 | 0 | 0 |
0 | 1 | 1 | 0 |
1 | 0 | 1 | 1 |
1 | 1 | 1 | 1 |
3. Draw the voltage current characteristics of a Zener diode.
Ans:
The voltage current characteristics of a Zener diode is as follows:

4. For an extrinsic semiconductor, indicate on the energy band diagram the donor and acceptor levels.
Ans: There are two types of extrinsic semiconductors: n-type extrinsic semiconductor and p-type extrinsic semiconductor. The energy band diagrams with the donor and acceptor levels are shown below:


5. What do you mean by depletion region and potential barrier in junction diode?
Ans: A layer around the intersection between p and n sections of a junction diode where charge carriers, electrons and holes are less in number is called the depletion region.
The potential difference created due to the diffusion of charge carriers across the junction is called the potential barrier.
6. A transistor has a current gain of
Ans:
Given that:
We also know that
Clearly, voltage gain
7. What are the advantages and disadvantages of semiconductor devices over vacuum tubes?
Ans:
Advantages:
Semiconductor devices are tiny in size as compared to vacuum tubes.
They need low voltage for their operation.
Disadvantages:
On the application of high voltage as well as increase in temperature, semiconductors can be damaged easily.
8. The base of a transistor is lightly doped. Explain why?
Ans: In a transistor, most carriers from the emitter region move towards the collector region through the base.
If the base is made thick and highly doped, most carriers will combine with the other carriers within the base, and only a few are collected by the collector, leading to a small output collector current.
Thus, to have a large output collector current, the base is made thin and lightly doped.
9. When similar diodes
a)

Ans:
In figure (i),
b)

Ans:
In figure (ii),
10. What do you mean by hole in a circuit? Write its two characteristics.
Ans: A vacancy formed in a covalent bond in a semiconductor due to the release of an electron is known as a hole in a semiconductor.
Characteristics of hole are:
a) The hole is equivalent to a positive electric charge.
b) The mobility of a hole is smaller than that of an electron.
11. Diode used in the figure has constant voltages drop at

Ans:
It is given that:
For the given circuit, applying Kirchhoff’s rules,
12. Zener diode has saturation current of

Ans:
Here,
Clearly,
Thus,
Now,
So, current
13. In an n-type Silicon, which of the following statement is true?
a) Electrons are majority carriers and trivalent atoms are the dopants.
b) Electrons are minority carriers and pentavalent atoms are the dopants.
c) Holes are minority carriers and pentavalent atoms are the dopants.
d) Holes are majority carriers and trivalent atoms are the dopants.
Ans:
The correct statement is (c).
In an n-type Silicon, the majority carriers are electrons while the minority carriers are the holes.
When pentavalent atoms, such as Phosphorus are doped with Silicon atoms, an n-type semiconductor is obtained.
14. Which of the statements given in Question 13 is true for p-type semiconductors?
Ans:
The correct statement is (d).
In an p-type silicon, the majority carriers are holes while the minority carriers are the electrons.
When trivalent atoms, such as Aluminium are doped in Silicon atoms, a p-type semiconductor is obtained.
15. Carbon, Silicon and Germanium have four valence electrons each. These are characterised by valence and conduction bands separated by energy band gap respectively equal to
a)
b)
c)
d)
Ans:
The correct statement is (c).
Out of the three given elements, the energy band gap of Carbon is the maximum, and Germanium's energy band gap is the minimum.
The energy band gaps of the given elements have the relation:
16. In an unbiased p-n junction, holes diffuse from the p-region to n-region because
a) Free electrons in the n-region attract them.
b) They move across the junction by the potential difference.
c) Hole concentration in p-region is more as compared to n-region.
d) All the above.
Ans:
The correct statement is (c).
The movement of charge carriers across a junction takes place from higher concentration to lower concentration.
In this case, the p-region has a higher concentration of holes than the n-region. Hence, in an unbiased p-n junction, holes move from the p-region to the n-region.
17. When a forward bias is applied to a p-n junction, it
a) raises the potential barrier.
b) reduces the majority carrier current to zero.
c) lowers the potential barrier.
d) None of the above.
Ans:
The correct statement is (c).
When a p-n junction is forward biased, it reduces the value of the potential barrier. In the case of forward bias, the potential barrier reverses the applied voltage. Therefore, the potential barrier across the junction gets decreased.
18. For transistor action, which of the following statements are correct?
a) Base, emitter and collector regions should have similar size and doping concentrations.
b) The base region must be very thin and lightly doped.
c) The emitter junction is forward biased and collector junction is reverse biased.
d) Both the emitter junction as well as the collector junction are forward biased.
Ans:
The correct statements are (b) and (c).
For smooth action of transistor, the base region needs to be lightly doped and very thin.
Also, the emitter junction should be forward-biased whereas the collector junction should be reverse-biased.
19. For a transistor amplifier, the voltage gain
a) remains constant for all frequencies.
b) is high at high and low frequencies and constant in the middle frequency range.
c) is low at high and low frequencies and constant at mid frequencies.
d) None of the above.
Ans:
The correct statement is (c).
The transistor amplifier's voltage gain is constant at the mid-frequency range only. It is low at high and low frequencies.
20. In half-wave rectification, what is the output frequency if the input frequency is
Ans:
Given that:
Input frequency
For a half-wave rectifier, the output frequency and the input frequency are equal.
Therefore, output frequency for a half wave rectifier
For a full-wave rectifier, the output frequency is the twice of the input frequency.
Therefore, output frequency for a full wave rectifier
3 Marks Questions
1. What is an ideal diode? Draw the output wave form across the load resistor

Ans:
An ideal diode provides zero resistance when it is forward biased and it offers an infinite resistance when it is reverse biased.
Output wave form across the load resistor

2. With the help of a labelled circuit diagram, explain full wave rectification using junction diode. Draw input and output wave forms.
Ans:
A full-wave rectifier comprises two diodes and a transformer with a central tap.
For any half cycle of AC input, only one diode is forward biased whereas the other one is reverse biased.


For positive half of AC input, diode
Thus, for both the half waves, output is obtained and the current moves in the same direction across load resistance
3. Name the gate shown in the figure and write its truth table?

Ans:
The given gate is an AND gate and its truth table is:
A | B | Y |
0 | 0 | 0 |
0 | 1 | 0 |
1 | 0 | 0 |
1 | 1 | 1 |
4. In the following diagrams indicate which of the diodes are forward biased and which are reverse bias?
a)

Ans:
It is forward biased because cathode is connected to higher potential so, current will move from p to n.
b)

Ans.
It is reverse biased because cathode is grounded and n is connected with higher potential so, current will flow from n to p.
c)

Ans:
It is forward biased because cathode is connected to higher potential so, current will move from p to n.
5. In the given figure, is

i. the emitter base is forward or reverse biased?
Ans.
Figure shows n-p-n transistor.
The emitter is reversed biased because the n-region is connected to a higher potential.
ii. collector base forward or reverse biased? Justify.
Ans:
The collector is also reversed biased because the n-region of the p-n junction is at a higher potential than the p-region.
6. Two semiconductor materials A and B shown in the figure are made by doping germanium crystal with arsenic and indium respectively. The two are joined end to end and connected to a battery as shown.

a) Will the junction be forward biased or reverse biased? Justify.
Ans:
Material A is n-type as it is doped with a pentavalent impurity and material B is p-type as it is doped with a trivalent impurity.
As a result, the junction becomes reverse biased because the battery's positive terminal is attached to the n-type and the battery's negative terminal is connected to the p-type. Hence it is reversed biased.
b) Sketch a V-I graph for this arrangement.
Ans.
V-I graph for the given circuit is given by:

7. Calculate emitter current for which
Ans:
Given:
Using
8. Draw the circuit diagram for common – emitter transistor characteristics using N-P-N transistor. Draw the input and output characteristic curve.
Ans:

Input characteristic curve gives the base current variation

Output characteristic curve gives the collector current variation

9. For a CE-transistor amplifier, the audio signal voltage across the collected resistance of
Ans:
Collector resistance,
Voltage across the collector resistance,
Current amplification factor of the transistor,
Base resistance,
Input signal voltage
Base current
Voltage amplification
Therefore, the input signal voltage of the amplifier is
Base current is given as:
Therefore, the base current of the amplifier is
10. Two amplifiers are connected one after the other in series (cascaded). The first amplifier has a voltage gain of
Ans:
Given:
Voltage gain of the first amplifier,
Voltage gain of the second amplifier,
Input signal voltage,
Output AC signal voltage
The total voltage gain of a two-stage cascaded amplifier is given by the product of voltage gains of both the stages, i.e.,
We have the relation:
Therefore, the output AC signal of the given amplifier is
11. A p-n photodiode is fabricated from a semiconductor with band gap of
Ans:
Energy band gap of the given photodiode,
Wavelength,
The energy of a signal is given by the relation:
Where,
But
The energy of a signal of wavelength
12. The number of Silicon atoms per
Ans:
Number of silicon atoms,
Number of arsenic atoms,
Number of indium atoms,
Number of thermally-generated electrons,
Number of electrons,
Number of holes
In thermal equilibrium, the concentrations of electrons and holes in a semiconductor are related as:
Therefore, the number of electrons is approximately
Since the number of electrons (
13. Write the truth table for a NAND gate connected as given in Fig. 14.45.

Hence identify the exact logic operation carried out by this circuit.
Ans:

Hence, the output will be:
The truth table for equation (i) can be drawn as:
0 | 1 |
1 | 0 |
This circuit acts as a NOT gate. The symbol for this logic circuit is shown as:

14. You are given two circuits as shown in Fig. 14.46, which consist of NAND gates. Identify the logic operation carried out by the two circuits.
a)

Ans:
In the given circuit,
The output of the first NAND gate will be

Clearly, the output of the combination of the two NAND gates is given as:
Hence, this circuit acts as an AND gate.
b)

Ans.
In the given circuit,

Hence, the output of the combination of the NAND gates will be given as:
Clearly, this circuit acts as an OR gate.
15. Write the truth table for circuit given in Fig. 14.47 below consisting of NOR gates and identify the logic operation (OR, AND, NOT) which this circuit is performing.

Ans:
The output of the first NOR gate is
It is observed from the given figure that the output of first NOR gate is the input of the second NOR gate.

Hence, the output of the combination is given as:
The truth table for this operation is given as:
A | B | Y=A+B |
0 | 0 | 0 |
0 | 1 | 1 |
1 | 0 | 1 |
1 | 1 | 1 |
This is the truth table of an OR gate. Hence, this circuit acts as an OR gate.
5 Marks Questions
1. Distinguish between conductors, insulators and semiconductors on the basis of energy band diagrams.
Ans:
Conductor – The conduction band in a conductor is either partially filled, or the conduction and valence band overlap each other. There is no energy gap in a conductor.

Insulators – The conduction band and valence band of all insulators are widely separated by an energy gap of the order about

Semiconductor – In semiconductors, the energy gap is tiny i.e., about 1eV only.

2. The following truth table gives the output of a 2 - input logic gate.
A | B | Output |
0 | 0 | 1 |
0 | 1 | 0 |
1 | 0 | 0 |
1 | 1 | 0 |
Identify the logic gate used and draw its logic symbol. If the output of this gate is fed as input to a NOT gate, name the new logic gate so formed.
Ans:
The gate is NOR gate. If the output of NOR gate is joined to a NOT gate then the obtained figure will be

New truth table is
0 | 0 | 0 |
0 | 1 | 1 |
1 | 0 | 1 |
1 | 1 | 1 |
This represents the truth table of OR gate.
3. With the help of a diagram, show the biasing of a light emitting diode (LED). Give its two advantages over conventional incandescent lamps.
Ans:
The light-emitting diode is forward biased, i.e., energy is released at the junction.

Advantages of LED over incandescent lamps are:
1) They are utilized in numerical displays.
2) It operates at low voltage and has a longer life than glowing bulbs.
4. The input resistance of a silicon transistor is
Ans:
Given:
Current gain is given by
5. Draw the symbol for Zener diode. Zener diodes have higher dopant densities as compared to ordinary p-n junction diodes. How does it affect the
i. width of the depletion layer?
Ans:
Symbol for Zener diode:

The width of depletion layer of the Zener diode becomes very small due to heavy doping of p and n-regions.
ii. junction field?
Ans.
The junction field of the Zener diode becomes very high due to heavy doping of p and n-regions.
6. A P-N-P transistor is used in common – emitter mode in an amplifier circuit. A change of
i. input resistance
Ans:
Given:
ii. current amplification factor
Ans.
Current amplification factor is given by
Here, it is given that load resistance
Voltage gain is given by
7. A semiconductor has equal electron and whole concentration of
i. Identify the new semiconductor
Ans:
New semiconductor obtained is N-type as
ii. Calculate the new hole concentration.
Ans.
It is known that
Clearly,
iii. How does the energy gap vary with doping?
Ans:
With doping, the energy gap decreases due to generated donor levels in between the valence band and the conduction band.
8. Draw a labelled circuit diagram of a common emitter transistor amplifier. Draw the input and the output wave forms and also state the relation between input and output signal?
Ans:
The circuit diagram of a common emitter transistor amplifier is:

Input wave form is:

Output wave form is:

There is
Also, the output is amplified compared to input waveform.
9. In an intrinsic semiconductor the energy gap
Ans:
Given:
Energy gap of the given intrinsic semiconductor,
The temperature dependence of the intrinsic carrier-concentration is given by:
Where
Initial temperature,
The intrinsic carrier-concentration at initial temperature is given as:
Final temperature,
The intrinsic carrier-concentration at final temperature is given as:
The ratio between the conductivities at
Therefore, the ratio between the conductivities is
10. In a p-n junction diode, the current I can be expressed as
a) What will be the forward current at a forward voltage of
Ans:
In a p-n junction diode, the current’s expression is given as:
Where,
Forward voltage
Therefore, the forward current is about
b) What will be the increase in the current if the voltage across the diode is increased to
Ans.
For forward voltage,
Hence, the increase in current
c) What is the dynamic resistance?
Ans.
Dynamic resistance
d) What will be the current if reverse bias voltage changes from
Ans.
If the reverse bias voltage varies from
11. You are given the two circuits as shown in Fig. 14.44. Show that circuit
a) acts as OR gate

Ans:
The left half acts as the NOR Gate while the right half of the given figure acts as the NOT Gate. This is shown in the following figure.

Hence, the output of the NOR Gate
This will be the input for the NOT Gate.
Its output will be
Hence, this circuit acts as an OR Gate.
b) acts as AND gate.

Ans.
It can be seen from the given figure that the inputs of the NOR Gate at the right half are the outputs of the two NOT Gates.

Hence, the output of the given circuit can be written as:
Hence, this circuit functions as an AND Gate.
12. Write the truth table for the circuits given in Fig. 14.48 consisting of NOR gates only. Identify the logic operations (OR, AND, NOT) performed by the two circuits.
a)

Ans:
Hence, the output of the following circuit is

Output
The truth table for the same is given as:
0 | 1 |
1 | 0 |
b)

Ans.
By utilizing the result obtained in solution (a), we can see that the outputs of the given first two NOR gates are

The truth table is:
0 | 0 | 0 |
0 | 1 | 0 |
1 | 0 | 0 |
1 | 1 | 1 |
It is the truth table of an AND gate. Hence, the circuit acts as an AND gate.
Important Formulas from Class 12 Physics Chapter 14 Semiconductor Electronic Material Devices and Simple Circuits
Conductivity of a Semiconductor:
Resistivity of a Semiconductor:
Drift Velocity:
Current in a p-n Junction Diode:
Depletion Region Width in p-n Junction:
Current Gain in Transistors:
Logic Gate Outputs (e.g., AND Gate):
Cutoff Frequency of Transistor:
Rectification Efficiency:
Benefits of Class 12 Physics Chapter 14 Semiconductor Electronic Material Devices and Simple Circuits
Chapter 14 of Class 12 Physics gives a detailed explanation about Semiconductors, n-type, and P-type semiconductors.
In this chapter, we mainly focused on definitions and meanings of minority charge carriers and majority charge carriers.
We learn about the different types of materials like conductors, insulators, and semiconductors. We come across the concept of the energy gap.
The method of doping, the importance of doping, a different type of dopants used in semiconductors is also covered in this chapter.
Different types of diodes like Pn-junction diodes, Zener diodes, etc… are studied along with their characteristics.
Tips to Study Class 12 Physics Chapter 14 Important Questions
Understand the properties of semiconductors and their types (intrinsic and extrinsic).
Memorize key formulas and their derivations for numerical problems.
Focus on the working principles of diodes, transistors, and logic gates.
Solve NCERT exercises and additional questions from reference books.
Practice drawing and analyzing circuit diagrams for clarity.
Study the practical applications of semiconductor devices in real-world scenarios.
Revise Boolean algebra for a better understanding of logic gates.
Related Study Materials for CBSE Class 12 Physics Chapter 14
S. No | Important Study Material Links for Class 12 Physics Chapter 14 |
1. | Class 12 Semiconductor Electronic Material Devices and Simple Circuits Notes |
2. | Class 12 Semiconductor Electronic Material Devices and Simple Circuits Solutions |
3. | Class 12 Semiconductor Electronic Material Devices and Simple Circuits Exemplar Solutions |
Conclusion
Semiconductor Electronics is an exciting and essential chapter 14 that bridges physics and practical electronics. By mastering the concepts and formulas, students can crack board exams and competitive tests. Utilise the Vedantu FREE PDF of important questions, practice diligently, and build a strong foundation in modern electronics!
Download CBSE Class 12 Physics Important Questions 2024-25 PDF
CBSE Class 12 Physics Chapter-wise Important Questions and Answers cover topics from all other chapters, helping students prepare thoroughly by focusing on key topics for easier revision.
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FAQs on Semiconductor Electronic Material Devices And Simple Circuits Class 12 Important Questions: CBSE Physics Chapter 14
1. What is the importance of Chapter 14 in Class 12 Physics?
Semiconductor Electronics is crucial for understanding modern electronic devices and their real-world applications, making it important for board exams and competitive exams.
2. What are the key concepts in NCERT Chapter 14 of Class 12 Physics?
The chapter covers semiconductors, p-n junctions, diodes, transistors, and logic gates.
3. What are the most important questions from Chapter 14 Class 12 Physics?
Derive the expression for drift velocity.
Explain the working of a Zener diode as a voltage regulator.
Describe the input and output characteristics of an NPN transistor.
4. How to effectively study logic gates in Chapter 14 Class 12 Physics?
Understand the truth tables, Boolean expressions, and practical applications of logic gates in digital circuits.
5. What is the significance of the p-n junction in semiconductors?
The p-n junction is a fundamental component in devices like diodes and transistors, controlling current flow and enabling rectification and switching.
6. How can I master the numerical problems in Chapter 14 Physics in Class 12?
Practice numerical from NCERT exercises and reference books, focusing on topics like drift velocity, resistivity, and circuit analysis.
7. How to approach important derivations in Semiconductor Electronics of Chapter 14?
Write and practice derivations like the diode equation and drift velocity to build a clear understanding and remember the steps.
8. What role do semiconductors play in everyday life in Chapter 14Class 12 Physics?
Semiconductors are the backbone of modern electronics, used in computers, smartphones, solar cells, and more.
9. Where can I find past year's important questions for Chapter 14 Class 12 Physics?
Past year questions are available in sample papers, board exam question banks, and online study materials are available at the Vedantu website.
10. How to download the FREE PDF of important questions for Chapter 14?
The FREE PDF can be downloaded from the Vedantu website which provides Class 12 study resources.











