NCERT Exemplar Solutions for CBSE Class 12 Physics: Chapter 14 - Semiconductor Electronics
NCERT Exemplar Solutions for Class 12 Physics, Chapter 14 (Semiconductor Electronics: Materials, Devices and Simple Circuits) are available here. This chapter is one of the most important chapters of Class 12 Physics NCERT textbook. Students can expect 2 to 3 questions from this chapter in their CBSE Class 12 Physics board exam 2018 (as per latest CBSE Class 12 Physics blueprint or examination pattern). One can also expect questions from NCERT Exemplar in CBSE board exams. So, in order to score well in board exams, CBSE Class 12 Students must practice questions from NCERT Exemplar.
The PDF (or eBook of) NCERT Exemplar Solutions for Class 12 Physics, Chapter 14 (Semiconductor Electronics: Materials, Devices and Simple Circuits) contains solutions for all the questions of this chapter.
This chapter contains:
• 8 MCQ I (Multiple choice questions with single correct option)
• 8 MCQ II (Multiple choice questions with multiple correct options)
• 6 VSA (Very short answer type questions)
• 8 SA (Short answer type questions)
• 10 LA (Long answer type questions)
Most of the questions are based on the topics given below:
• Energy bands in conductors
• Semiconductors and insulators
• Semiconductor diode: I-V characteristics in forward and reverse bias
• Diode as a rectifier
• Special purpose p-n junction diodes:
• Zener diode and their characteristics
• Zener diode as a voltage regulator
• Junction transistor
• Transistor action
• Characteristics of a transistor
• Transistor as an amplifier (common emitter configuration)
• Analog and digital signals
• Logic gates (OR, AND, NOT, NAND and NOR)
From ongoing trends of CBSE Board exams and other competitive exams (like JEE Main, NEET, UPSEE, WBJEE etc), we have observed that questions are frequently asked from Chapter 14 - Semiconductor Electronics (Semiconductor Electronics: Materials, Devices and Simple Circuits). Hence, there is no doubt that problems given in NCERT Exemplar are important for both board exam and competitive exams. The level of NCERT Exemplar questions is quite high and all the questions are important for CBSE Class 12 Physics board exam 2018.
Some problems and solutions from the chapter are given below:
The conductivity of a semiconductor increases with increase in temperature, because
(a) number density of free current carries increases
(b) relaxation time increases
(c) both number density of carries and relaxation time increase
(d) number density of carries increases, relaxation time decreases but effect of decrease in relaxation time is much less than increase in number density
With increase in temperature, the number density of current carries increases, relaxation time decreases but effect of decrease in relaxation is much less than increase in number density. So, the conductivity of a semiconductor increases with increase in temperature.
(a) an anti-particle of electron
(b) a vacancy created when an electron leaves a covalent bond
(c) absence of free electrons
(d) an artificially created particle
Hole can be defined as a vacancy created when an electron leaves a covalent bond.
Hole is a concept which is the lack of an electron at a position where one could exist in an atom or atomic lattice. If an electron is excited into a higher state, it leaves a hole in its old state.
When an electric field is applied across a semiconductor
(a) electrons move from lower energy level to higher energy level in the conduction band
(b) electrons move from higher energy level to lower energy level in the conduction band
(c) holes in the valence band move from higher energy level to lower energy level
(d) holes in the valence band move from lower energy level to higher energy level
Solution: (a, c)
As we apply electric field is applied across a semiconductor, the electrons in the conduction band acquire energy and get accelerated. They travel from lower energy level to higher energy level. While the holes in valence band travel from higher energy level to lower energy level, where they will be having more energy.
Consider a n-p-n transitor with its base-emitter junction forward biased and collector base junction reverse biased. Which of the following statements are true?
(a) Electrons crossover from emitter to collector
(b) Holes move from base to collector
(c) Electrons move from emitter to base
(d) Electrons from emitter move out of base without going to the collector.
Solution: (a, c)
In an n-p-n transitor, Emitter-base junction is forward biased, when the positive pole of emitter base battery is connected to the base and its negative pole to the emitter.
Also, the collector base junction is reverse biased, when, the positive pole of the collector base battery is connected to collector and negative pole to the base. So, electrons move from emmiter to base and crossover from emitter to collector.
In the depletion region of a diode
(a) there are no mobile charges
(b) equal number of holes and elections exist, making the region neutral
(c) recombination of holes and electrons has taken place
(d) immobile charged ions exist
Solution: (a, b, d)
The space-charge regions on both the sides of p-n junction which has immobile ions and entirely lacking of any charge carriers will form a region called depletion region of a diode. The number of ionized acceptors on the p-side equals the number of ionized donors on the n-side.
What happens during regulation action of a Zener diode?
(a) The current and voltage across the Zener remains fixed
(b) The current through the series Resistance (Rs) changes
(c) The Zener resistance is constant
(d) The resistance offered by the Zener changes
Solution: (b, d)
The current through the Zener changes but the voltage across the Zener remains constant. Therefore, during regulation action of a Zener diode, the current through the Rs changes and resistance offered by the Zener changes.
The breakdown in a reverse biased p-n junction is more likely to occur due to
(a) large velocity of the minority charge carriers if the doping concentration is small
(b) large velocity of the minority charge carriers if the doping concentration is large
(c) strong electric field in a depletion region if the doping concentration is small
(d) strong electric field in the depletion region if the doping concentration is large
Solution: (a, d)
In case of reverse biasing, the minority charge carriers will be accelerated due to reverse biasing, which on striking with atoms cause ionization resulting more number of secondary electrons & thus more number of charge carriers.
If doping concentration is large, there will be large number of ions in the depletion region, which will give rise to a strong electric field.
Detailed explanations of each and every question of the chapter are given in the PDF.