Case Study Questions Class 12 Physics Chapter 14 Semiconductor electronics: Materials, Devices and Simple Circuits
CBSE Class 12 Case Study Questions Physics Semiconductor electronics: Materials, Devices and Simple Circuits. Term 2 Important Case Study Questions for Class 12 Board Exam Students. Here we have arranged some Important Case Base Questions for students who are searching for Paragraph Based Questions Semiconductor electronics: Materials, Devices and Simple Circuits.
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CBSE Case Study Questions Class 12 Physics Semiconductor electronics: Materials, Devices and Simple Circuits
Case study 1:
Materials are classified on the basis of their conductivity as metals, semiconductors and insulators. Metals are having low resistivity and high conductivity. While semiconductors are having resistivity and conductivity in between metals and insulators. And finally insulators are those which are having high resistivity or very low conductivity. Semiconductors may exist as elemental semiconductors and also compound semiconductors. Si and Ge are elemental semiconductor and CdS, GaAs, CdSe, anthracene, polypyrrole etc. are the compound semiconductors. Each electron in an atom has different energy level and such different energy levels continuing forms the band of energy called as energy bands. Those energy band which has energy levels of Valence electrons is called as Valence band. And the energy band which is present above the Valence band is called as conduction band. On the basis of energy bands materials are also defined as metals, semiconductors and insulators. In case of metals, conduction band and Valence band overlaps with each other due to which electrons are easily available for conduction. In case of insulators, there is some energy gap between conduction band and Valence band due to which no free electrons are easily available for conduction. And in semiconductors, there is a small energy gap between conduction band and Valence band and if we give some external energy then electron from Valence band goes to conduction band due to which conduction will be possible. These semiconductors are classified as intrinsic semiconductors and extrinsic semiconductors also. Intrinsic semiconductors are those semiconductors which exist in pure form. And intrinsic semiconductors has number of free electron is equal to number of holes. The semiconductors doped with some impurity in order to increase its conductivity are called as extrinsic semiconductors. Two types of dopants are used they are trivalent impurity and pentavalent impurity also. The extrinsic semiconductors doped with pentavalent impurity like Arsenic, Antimony, Phosphorus etc are called as n – type semiconductors. In n type semiconductors electrons are the majority charge carriers and holes are the minority charge carriers. When trivalent impurity is like Indium, Boron, Aluminium etc are added to extrinsic semiconductors then p type semiconductors will be formed. In p type semiconductors holes are majority charge carriers and electrons are the minority charge carriers.
Questions:
Q 1.) In case of p-type semiconductors___
a) nh<< ne
b) nh = ne
c) nh>> ne
d) nh= ne = 0
Q 2.) An intrinsic semiconductor behaves like _____ at T = 0K.
a) conductor
b) metal
c) non metal
d) insulator
Q 3.) If the energy band gap Eg> 3 eV then such materials are called as
a) conductors
b) semiconductors
c) insulators
d) superconductors
Q 4.) What is energy band gap in case of materials?
Q 5.) How p-type and n-type semiconductors are formed?
Answer key:
Q 1.) c) nh>> ne
Q 2.) d) insulator
Q 3.) c) insulators
Q 4.) The energy difference between top of the Valence band and bottom of the conduction band is called as energy band gap. On the basis of energy band gap materials are also classified. Metals are having nearly zero energy band gap. Semiconductors are having 0.2 eV to 3 eV energy band gap. And insulators are having energy band gap more than 3eV.
Q 5.) When trivalent impurity like B, Al, In are added to extrinsic semiconductor like Ge or Si then p-type Ge or Si semiconductor is formed. And when pentavalent impurity like As, Sb, P are added to extrinsic semiconductors like Ge or Si then n-type Ge or Si semiconductor is formed.
Case study 2:
When p side of p-n junction is connected to positive terminal of battery and n side of p-n junction is connected to negative terminal of battery then the p-n junction is said to be in forward bias mode or forward biased. And When p side of p-n junction is connected to negative terminal of battery and n side of p-n junction is connected to positive terminal of battery then the p-n junction is said to be in reverse bias mode or reverse biased. The diode used to rectify an AC voltage is called as rectifier. Zener diode is also a p-n junction diode which works in reverse bias condition and used as voltage regulator. Also, p-n junction diodes are used in solar cells which is used to convert light energy into electrical energy. Light emitting diodes are also p-n junction diodes which are used to produce light. The digital circuit which gives the logical relationship between input and output voltage are called as logic gates. There are five basic gates namely NOT, AND, OR, NAND, NOR.
NOT gate is that logic gate which gives inverted input as output such as if 1 is the input given then output will be 0. The other logic gates OR, AND, NAND, NOR has two inputs and only one output.
Questions:
Q 1.) Zener diode and photodiode works in the ____ .
a) forward bias mode
b) reverse bias mode
c) both a and b
d) none
Q 2.) The semiconductors which are used to make visible LEDs must have band gap of ___
a) 3 eV
b) 0 eV
c) 1.8 eV
d) 5 eV
Q 3.) The rectifier in which the rectified output is only for half of the input AC wave is called as___
a) full wave rectifier
b) half wave rectifier
c) transformer
d) transducer
Q 4.) What is dynamic resistance?
Q 5.) What is barrier potential?
Answer key:
Q 1.) b) reverse bias mode
Q 2.) c) 1.8 eV
Q 3.) b) half wave rectifier
Q 4.) The ratio of small change in voltage ∆V to a small change in current ∆I is called as dynamic resistance and is given by
rd= ∆V/ ∆I
Q 5.) The electric potential required to restrict the movement of electron from n-side to p-side across p-n junction is called as barrier potential.