MCQs on Analog Electronics


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01․ What will happen if doping of an intrinsic semiconductor with pentavalent impurity atom ?
Fermi level not change
Fermi level fall
Fermi level raises
None of the above

When the donor density is increased, the Fermi level moves closer to the edge of the conduction band.

02․ Silicon has
four valence electrons.
eight valence electrons.
two valence electrons.
none of above.

A semi-conductor has 4 valence electrons. Silicon is semi-conductor. So, the valence electrons of Silicon are 4. Atomic number of silicon is 14. so its configuration is (2 8 4). The last 4 electrons acts as a valance band.

03․ Germanium has
ionic bond.
covalent bond.
molecular bond.
metallic bond.

A covalent bond is the chemical bond that involves the sharing of pairs of electrons between atoms. In the electronic configuration of germanium crystals there are four valence electrons. These four electrons will form covalent bonds, with the neighboring electrons of the germanium atoms. Each covalent bond is formed by sharing each electron from the each atom. After bond formation, no free electron will remain in the outermost shell of the germanium semi conductor.

04․ Energy gap of conductor is
1 - 2 eV.
0 eV.
5 - 8 eV.
8 eV.

Energy gap is the gap between conduction band and valance band. Energy gap Eg of conductor is 0 eV since it has overlapped valance and conduction band.

05․ Energy gap of semiconductor is approx
1 eV.
0 eV.
5 - 8 eV.
> 8 eV .

Energy gap is the gap between conduction band and valance band. Energy gap Eg of the semiconductor is relatively small around 1 eV.

06․ Why is silicon preferred than germanium ?
Leakage current due to minority charge carrier is less in silicon
Current sensitivity of silicon with temperature is less
Silicon has higher tolerance to temperature
All the above

Silicon is more preferred than germanium while manufacturing the semiconductor devices because of the following reasons: i. The current sensitivity of silicon with temperature is less than that in germanium. ii. Silicon has higher tolerance to temperature than germanium. iii. The leakage current due to minority charge carrier is less in silicon than that in germanium.

07․ Why holes are not created in a metal ?
The forbidden band is missing
The conduction band and valance band are overlapped
Both 1 & 2
None of the above

In a conductor, the forbidden band is missing and the conduction band and valance band are overlapped. Therefore, no holes can be created in a metal.

08․ Which is the pair of acceptor elements ?
Gallium and boron
Antimony and indium
Phosphorous and aluminium
None of the above

When boron or aluminum atoms that have three bonds accept an electron pair from Gallium.

09․ A Semiconductor has a
Negative Temperature coefficient of resistance
Positive Temperature coefficient of resistance
Constant Temperature coefficient of resistance
None of the above

Negative Temperature coefficient of resistance means, the resistance of the material decrease with increase in temperature. Due to this property semiconductor behave like an insulator at very low temperature but act as a conductor at high temperature.

10․ The most commonly used semiconductor is
Carbon
Germanium
Sulphur
Silicon

The maximum working temperature of Germanium is 75° but silicon can be operated up to 150°. Another reason for choosing silicon is its knee voltage, the knee voltage of silicon is .7 V, whereas the knee voltage of germanium is .3 V.

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