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Published on: 23/05/2021
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Download CBSE Class 12th Standard CBSE Physics question papers, sample papers, important questions, and previous year solved papers in PDF format. Get free study materials, NCERT solutions, and exam preparation resources for Class 12th Standard CBSE Physics
Questions + Answers key
Take MCQ Physics Test1.
Why are elemental dopants for silicon or germanium usually chosen from group XIII or group XV ?
2.
Sn, C and Si, Ge are all group XIV elements. Yet, Sn is a conductor, C is an insulator while Si and Ge are semiconductors. Why?
3.
Write the truth table for the following circuit. Name the equivalent gate that this circuit.

4.
In a CE transistor amplifier, there is a current and voltage again associated with the circuit.In other words, there is a power gain.Considering power a measure of energy, does the circuit violate conservation of energy?
5.
Draw the output waveform across the resistor in the given figure

1.
The size of the dopant atom should be such that their presence in the pure semiconductor does not distort the semiconductor but easily contribute the charge carriers on forming covalent bonds with Si or Ge atoms, which are provided by group XIII or group XV elements.
2.
A material is a conductor, if in its energy band diagram, there is no energy gap between conduction band and valence band. For insulator, the energy gap is large and for semiconductor, the energy gap is moderate.
The energy gap for Sn is 0 eV, for C is 5.4 eV, for Si is 1.1 eV and for Ge is 0.7 eV, related to their atomic size. Therefore, Sn is a conductor, C is an insulator and Ge and Si are semiconductors.
3.
The given combination consists of NOR gate and NOT gate, so equivalent gate is OR gate.
Truth Table
| A | B | Y = A + B |
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 1 |
From the truth table, it is clear that the output is 1 only when atleast one of the inputs is at the high state(i.e.1).
4.
In CE transistor amplifier, the power gain is very high. In this circuit, the extra power required for amplified output is obtained from DC source. Thus, the circuit used does not violate the law of conservation of energy.
5.
As, we know that the diode only works in forward biased, so the output is obtained only when positive input is given, so the output waveform is

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