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# NCERT Exemplar Class 12 Physics Chapter 14 Solutions: Semiconductor Electronic: Material, Devices And Simple Circuits

NCERT Exemplar Class 12 Physics Solutions Chapter 14 is an important chapter for students who are appearing for CBSE or other competitive exams. This chapter of NCERT Exemplar Class 12 Physics discusses many key topics which are useful even in higher studies like engineering. It covers semiconductors and its types like intrinsic and extrinsic semiconductors, semiconductor diode and its applications, P-n junction, n-type and p-type semiconductors, junction transistor and application of junction diode as a rectifier, logic gates & digital electronics. All the topics have detailed questions covering all parts of the chapter.

When you solve exemplar problems of NCERT Class 12 Physics, you get acquainted with many types of questions like MCQs or objective type questions, short and long answers, fill in the blanks and true/false questions. It has a total of 40 questions which are spread across 5 sections.

Instasolv aims at not only providing solutions to these problems but also equipping students with many shortcut ways of remembering important formulae. By breaking down a complex problem into simple steps and explaining every detail of arriving at the solution, we help students to score better in the CBSE Class 12 Board exams.

## Important Topics for NCERT Science Exemplar Solutions Class 12 Chapter 14

• Basics of Semiconductors – Any material which can conduct electricity within certain conditions is a semiconductor. Its resistivity level is between that of a conductor and an insulator. They have common use in many electronic devices like transistors and diodes. Materials like silicon, germanium are examples of semiconductors. Some of the properties of semiconductors are:
• With an increase in temperature the resistance of a semiconductor decreases.
• If a metallic impurity is added to a semiconductor, which is suitable to it, its conducting property changes
• Valence electron – Electrons in the outermost shell are loosely attached to the nucleus and are called valence electrons.
• Electron pairs and Covalent bonds– An atom which has valence electrons can combine with valence electrons of another atom to form an electron pair. It is not a strong bonding and is termed as Covalent bond.
• Hole – When heat is supplied to a semiconductor, its covalent bond is broken and the electrons move away. This moving away of electrons creates a hole which is considered as a unit positive charge and the left behind electron is the negative charge. So when an electric field is applied, the liberated electron moves in a direction opposite to the applied field while the hole moves towards the field. This moving of hole makes a hole current.
• Doping – When impurity is added to a semiconductor, it is called doping.
• Pentavalent impurities – An impurity with 5 valence electrons in its outer orbit is a pentavalent impurity. It is a donor atom as it donates one electron to the pure semiconductor atom. E.g.: Bismuth, Phosphorus.
• Trivalent impurities – An impurity with 3 valence electrons in its outer orbit is a trivalent impurity. It is an acceptor atom as it accepts one electron to the pure semiconductor atom. E.g.: Aluminum, Boron.
• Types of semiconductors –
• Pure or intrinsic semiconductors – A semiconductor which is undoped and is in its extremely pure form is an intrinsic semiconductor. In this:
• Number of holes = number of free electrons
• Conduction capability is less at room temperature
• Electrons and holes are created only by thermal excitation

ne = nh = ni

Here ne  = free electron density in conduction band

nh = hole density in valence band

ni = intrinsic carrier concentration

• Impure or Extrinsic Semiconductors – By doping an intrinsic semiconductor one gets an extrinsic semiconductor.

ne nh = ni2

Based on the type of impurity added, extrinsic semiconductors are categorized in 2 types:

• N-Type semiconductors – When a Pentavalent impurity is added to a pure semiconductor, it forms an N-type semiconductor. The electrons thus added provide conduction. Electrons are the majority carriers here and holes are the minority carriers of electricity. In the event of an electric field applied to an n-type, free electrons move towards the positive electrode and create a negative conductivity.

ne = nd nh

Here nd is number density of donor atom.

• P-type semiconductors – When a trivalent impurity is added to a pure semiconductor, it forms an P-type semiconductor. The holes thus added provide hole current. Holes are the majority carriers here and electrons are the minority carriers of electricity. In the event of an electric field applied to a p-type, holes move towards the negative electrode creating a P-type conductivity.

Na = nhne

Here Na is the number density of acceptor atoms.

• Logic Gates – In digital devices, the input and output voltages follow a certain logic using a digital circuit. This controls the flow of information and called logic gates. It has a symbol and a truth table displaying all input-output combinations. Logic gates are made using semiconductor devices. The most common logic gates are:
1. NOT – A NOT gate has one input and one output and it inverts the input signal.
2. OR – An OR gate has 2 or more inputs and single output. We get an output of 1 if any one of the inputs is 1.
3. AND – An AND gate has 2 or more inputs and single output. We get an output of 1 if all the inputs are 1.
4. NAND – An AND gate followed by a NOT gate is a NAND gate. It means we get a 1 if all the inputs are not 1.
5. NOR – A NOR gate is an OR gate followed by a NOT gate. It means we get a 1 if all the inputs are 0.
• P-n junction – The n-type and p-type semiconductors are electrically neutral. By joining them a p-n junction is created which causes a large density gradient. The free electrons of n-type start drifting towards p-type holes and produce negative ions. The n-type now has positively charged donor ions due to electrons migration towards p-type. As a result of these movements of donors and acceptors, the P-type gets filled with negative charge along the junction and the n-type charge becomes positive along the junction, this charge transfer is called diffusion. At some point, equilibrium is reached when the total charge on either side of the p-n junction is equal and opposite so as to have a neutral charge condition around the junction. This area around the junction is called the depletion layer.

DpNa = DnND

Here D – depletion layer distance

Dp – Distance on the positive side

Dn – distance on the negative side

• Forward Bias – When a voltage is put across a diode which allows flow of current in one direction it is known as a forward bias.
• Junction diode as a rectifierJunction diodes can be used as a rectifier to convert AC into DC. When an AC is applied in a junction diode it allows current only in the parts where it is forward bias. This property makes it a rectifier.

## Discussion of Exercises of NCERT Exemplar Class 12 Physics Solutions Chapter 14

1. The first set of questions, MCQ1, is objective type questions with a single correct answer. It has 8 questions. They brush up topics on basics of semiconductors by analyzing different types of circuits, p-n junction, forward/reverse bias and types of rectifiers.
2. The second set of questions is MCQ2, which are again objective type questions where there may be more than 1 correct answer and you must choose all the correct answers for the given problem statement. It has 8 questions based on fundamental principles of a semiconductor, transistors, p-n junction, diodes, and rectifiers and capacitors.
3. The third set of questions requires very short type answers which touch areas like doping and various groups of semiconductor elements, p-n junction, resistors and drawing diagrams for their waveforms, and amplifiers. It has 6 questions.
4. The fourth set of questions requires short type answers where you need to apply knowledge of types of diodes, resistance and formulae around them, logic gates and truth tables to solve the 8 questions provided.
5. The fifth set of questions involves long answers and tests your expertise on solving problems related to forward bias resistance, voltage and resistance formula, logic gates, transistors, diodes, doping, and V-I graphs to solve the 10 questions presented.
6. The NCERT Exemplar Problems for all chapters of Physics are formulated after extensive research and it is highly likely that one would find questions from these books in many competitive exams.

## Why Use NCERT Science Exemplar Solutions Class 12 Chapter 14 by Instasolv?

Instasolv has provided NCERT Exemplar Class 12 Problems with Solutions by its team of subject matter experts who have an in-depth knowledge on every topic. Since those providing the solution are masters in that topic, they are well aware of difficulties that students might face while understanding a complex concept.

Hence the Exemplar solutions provided are easy to understand with a systematic approach. These free of cost solutions are extremely beneficial for students to grasp the subject as well as learn how to better time management in the exam hall.

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