HSSC-II (Class-12) Solved Physics MCQs; Unit-16: Physics of Solids (Baluchistan Textbook Board, Quetta) With Verified Answers: 


1. A geranium at 0K is




... Answer is C. Insulator
In pure form and at low temperatures i.e. at 0K the covalent bonds among the atoms are very strong and there is no free electron to jump from the valance band to the conduction band.


2. By increasing the temperature, the conductivity of the semiconductor is




... Answer is B. Increased
The electrical conductivity of semiconductors at room temperature is small. The conductivity increases with increasing temperature (i.e the more covalent bonds break and the more free electrons)


3. Which one of the following is an intrinsic semiconductor?




... Answer is D. Silicon
A pure semiconductor without any significant impurity or dopant species added is called an Intrinsic semiconductor


4. In extrinsic semiconductors, the doping level should be in the ratio




... Answer is D. 1:10⁸
It means there should be only one atom of impurity in 10⁸ atoms of pure semiconductor.


5.  In P-type semiconductors, the doping of silicon is taken place with




... Answer is B. Trivalent
When an impurity of a trivalent (valency 3) element like boron (B), gallium (Ga), Indium (In), etc. is added to a pure semiconductor (germanium, silicon) in a specific ratio then such a doped semiconductor is called a P-type semiconductor​


6. When P-type and N-type semiconductors are combined then we have a




... Answer is C. Diode
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7. The depletion region in PN-Junction carries :




... Answer is B. No mobile charge carrier
The depletion layer acts like a barrier that opposes the flow of electrons from the n-side and holes from the p-side ie. No mobile charge carrier


8. The potential difference across the silicon PN junction is




... Answer is C. 0.7 V
---------------


9. When the P-type of the PN-Junction is connected with the negative terminal and the N-type with the positive terminal of the battery, the width of the depletion region




... Answer is B. increases
This connection is called Reversed biased PN junction and here the majority of carriers of each region are attracted by the terminals of the battery. Thus the width of the depletion is further increased


10. In forward biasing, the knee voltage for Germanium PN-Junction is




... Answer is A. 0.3 V
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11. One of the most important properties of the diode




... Answer is A. Allow current in one direction
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12. The number of diodes used in a bridge rectifier is




... Answer is D. Four
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13. Transistor stands for




    ... Answer is A. Transfer of Resistance
    -----------------


    14.  Which region of the transistor is most widespread in terms of area?




    ... Answer is C. Collector
    The collector region of the transistor is made physically large and the base is very thin (base length is of the order of 10⁻⁶ m)


    15. In biasing of a transistor, which region must be reverse biased?




    ... Answer is B. Collector-Base
    The emitter-base junction is forward-biased and the collector-base is reversed biased


    16.. The thickness of the base region of a transistor is




    ... Answer is C. 10⁻⁶ m
    ---------------------


    17. Which one of the following relations is true for a transistor? :




    ... Answer is C. ∝ = `\frac {I_C}{I_E}`
    ----------------


    18. Which one of the following relations holds for the cutoff' mode of the transistor?




    ... Answer is D. `\I_C` = 0
    When the emitter-base junction is reversed ( ie cutoff mode), the base current is zero. the collector current is also zero


    19. The flow of charge carriers in a transistor is controlled by




    ... Answer is B. Base
    ---------------


    20. If the base current of a silicon transistor is 0.01mA, its collector current is




    ... Answer is D. 1 mA
    -----------------------


    21. `\V_{CE}` drops across the load resistor of a transistor when




    ... Answer is D. `\I_C` = β`\I_B`
    --------------------------


    22. When a transistor starts working in its active region




    ... Answer is B. After its saturation
    ------------------


    23. A transistor is used as a switch when it operates in its




    ... Answer is D. Saturation and cutoff mode
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