Maharashtra Board Class 11 Physics Chapter 14 Semiconductors Solution

Maharashtra Board Class 11 Physics Solution Chapter 14 – Semiconductors

Balbharati Maharashtra Board Class 11 Physics Solution Chapter 14: Semiconductors. Marathi or English Medium Students of Class 11 get here Semiconductors full Exercise Solution.

Std

Maharashtra Class 11
Subject

Physics

Chapter

14
Chapter Name

Semiconductors


1.) Choose the correct option.

i) Electric conduction through a semiconductor is due to:

(A) electrons

(B) holes

(C) none of these

(D) both electrons and holes

Answer- D

Depending upon type of semiconductor both electrons and holes are responsible for electric conduction.

ii) The energy levels of holes are:

(A) in the valence band

(B) in the conduction band

(C) in the band gap but close to valence band

(D) in the band gap but close to conduction band

Answer- C

For electrons it is in close to conduction band but for holes it is in the band gap but close to valence band.

iii) Current through a reverse biased p-n junction, increases abruptly at:

(A) Breakdown voltage

(B) 0.0 V

(C) 0.3V

(D) 0.7V

Answer- A

iv) A reverse biased diode is equivalent to:

(A) an off switch

(B) an on switch

(C) a low resistance

(D) none of the above

Answer- A

In reverse bias the width of depletion layer is increases and it behaves as a high resistance hence acts like an off switch.

v) The potential barrier in p-n diode is due to:

(A) Depletion of positive charges near the junction

(B) Accumulation of positive charges near the junction

(C) Depletion of negative charges near the junction,

(D) Accumulation of positive and negative charges near the junction

Answer- D

Potential barrier in p-n junction diode is because of Accumulation of positive and negative charges near the junction.

2.) Answer the following questions.

i) What is the importance of energy gap in a semiconductor?

Answer-energy gap in solids plays important role in distinguishing between conductor, semiconductor and insulator. Magnitude of band gap decides electronic properties of semiconductor.

ii) Which element would you use as an impurity to make germanium an n-type semiconductor?

Answer- pentavalent impurities like antimony or phosphorus can be used as an impurity to make germanium an n-type semiconductor.

iii) What causes a larger current through a p-n junction diode when forward biased?

Answer- in forward bias, p-n junction shows low resistance as width of depletion layer decreases due to forward biasing leads to cause larger current through diode.

iv) On which factors does the electrical conductivity of a pure semiconductor depend at a given temperature?

Answer-electricity depends upon number of charge carriers in the semiconductor as in case of pure semiconductor number of electrons equal to number of holes.

v) Why is the conductivity of a n-type semiconductor greater than that of p-type semiconductor even when both of these have same level of doping?

Answer- conductivity of n type of semiconductor is due to movement of free electrons while conductivity of p type is due to movement of holes. But as drift velocity of free electrons is more in case of n type than p type therefore conductivity of a n-type semiconductor greater than that of p-type semiconductor even when both of these have same level of doping.

3.) Answer in detail.

i) Explain how solids are classified on the basis of band theory of solids.

Answer- on the basis of band theory solids are classified as conductor, semiconductor and insulator. In solids two bands exist one is valence band and other is conduction band. When electrons in valence band gets extra energy they are raised to higher level overcoming energy gap called conduction band.

In conductors the valence band and the conduction band overlap and there is no band gap therefore conductors are good conductor of electricity.

In case of semiconductors, the band gap is small, of the order of one electron volt or less. When electrons given energy more than energy gap they can easily gain energy and go in conduction band easily and can conduct electricity.

In insulators this energy gap is large as compare to semiconductors hence electrons cant overcome energy gap easily therefore insulators are not electricity conductors as electrons cant go to conduction band.

ii) Distinguish between intrinsic semiconductors and extrinsic semiconductors.

Answer-

Sr no. Intrinsic semiconductor extrinsic semiconductor
It is pure semiconductor It is impure semiconductor as it is the result of mixing of impurity.
It is having low conductivity It is having high conductivity
as it is pure so number of electrons and holes are equal. as it is not pure so number of electrons and holes are unequal.
Conductivity depends upon temperature only Conductivity depends on temperature and amount of doping of impurity in semiconductor. More the dopinfg more the conductivity.

iii) Explain the importance of the depletion region in a p-n junction diode.

Answer- depletion layer is the region in p-n junction lies between p type region and n type region where there is no charges. Potential barrier is developed by depletion layer across junction who maintained equilibrium of junction.

If depletion layer is absent, all majority charge carriers from p region will get combined with electrons in n region result in decrease in efficiency of p-n junction diode. Therefore deplection layer is needed to maintain equilibrium and to limit carriers to cross the junction.

iv) Explain the I-V characteristic of a forward biased junction diode.

Answer-

Figure shows I-V characteristic of a forward biased junction diode and following observations are notted.

  1. Initially very small current flows through diode upto certain voltage.
  2. For silicon, at the voltage 0.7 V there is sudden rise in current flowing through diode this point is called as knee point.
  3. Above knee point diode goes in forward biased region and start conducting large current.
  4. To control this large current resistors in series are used with diodes.

v) Discuss the effect of external voltage on the width of depletion region of a p-n junction

Answer-

External voltage can be applied to p-n junction diode in forward bias and reverse bias mode.

In forward bias mode, p region is connected to positive terminal and n region to negative terminal. In this mode the external voltage opposes the barrier potential at junction thereby reducing width of depletion layer.

In reverse bias mode, p region is connected to negative terminal and n region to positive terminal. In this mode the external voltage adds to the barrier potential at junction thereby increasing width of depletion layer.


Updated: April 23, 2022 — 11:47 pm

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