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Electronics and Communication Engineering - Electromagnetic Field Theory

Exercise : Electromagnetic Field Theory - Section 3
16.
In which material do conduction and valence bands overlap
insulators
conductors
both conductor and semiconductor
semiconductors
Answer: Option
Explanation:

This is the reason for high conductivity of conductors.

17.
For a photoconductor with equal electron and hole mobilities and perfect ohmic contacts at the ends, an increase in illumination results in
a change in O.C. voltage
a change in S.C. current
a decrease in resistance
an increase in resistance
Answer: Option
Explanation:

Increase in illumination reduces resistance of a photoconductor.

18.
Discrete transistors T1 and T2 having maximum collector current rating of 0.75 amp are connected in parallel as shown in the figure, this combination is treated as a single transistor to carry a total current of 1 ampere, when biased with self bias circuit. When the circuit is switched on, T1 draws 0.55 amps and T2 draws 0.45 amps. If the supply is kept on continuously, ultimately it is very likely that
Both T1, and T2 get damaged
Both T1, and T2 will be safe.
T1 Will get damaged and T2 will be safe
T2 will get damaged and T1, will be safe.
Answer: Option
Explanation:

T1 draws 0.55 A and T2 draws 0.45 A, T1 will get more heated and correct increase. Ultimately, I1 = 1A and I2 = 0.

19.
The number of p-n junctions in a semiconductor diode are
0
1
2
1 or 2
Answer: Option
Explanation:

Semiconductor diode has one p-n junction, BJT has two and SCR has three p-n junctions.

20.

Assertion (A): A high junction temperature may destroy a diode.

Reason (R): As temperature increases the reverse saturation current increases.

Both A and R are true and R is correct explanation of A
Both A and R are true but R is not a correct explanation of A
A is true but R is false
A is false but R is true
Answer: Option
Explanation:

Both A and R are correct. The diode is destroyed due to high reverse current.

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