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Electronics and Communication Engineering - Electromagnetic Field Theory

Exercise : Electromagnetic Field Theory - Section 2
26.
The mean free path of conduction electrons in copper is about 4 x 10-8 m. For a copper block, find the electric field which can give, on an average, 1 eV energy to a conduction electron
2.62 x 107 V/m
2.64 x 107 V/m
2.5 x 107 V/m
2.58 x 107 V/m
Answer: Option
Explanation:

Work (Energy) = F x d

1 eV = e.E x d

2.5 x 107 V/m.

27.
When a p-n-p transistor is properly biased to operate in active region the holes from emitter.
diffuse through base into collector region
recombine with electrons in base
recombine with electrons in emitter
none of the above
Answer: Option
Explanation:

The reason that collector current is nearly equal to emitter current.

28.

Assertion (A): Silicon is preferred over germanium in manufacture of semiconductor devices.

Reason (R): Forbidden gap in silicon is more than that in germanium.

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:

Wider forbidden gap in silicon makes it less sensitive to temperature than germanium.

29.

Assertion (A): A decrease in temperature increases the reverse saturation current in a p-n diode.

Reason (R): When a diode is reverse biased surface leakage current flows.

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:

A is wrong because decrease in junction temperature decreases reverse saturation current.

30.
At room temperature a semiconductor material is
perfect insulator
conductor
slightly conducting
any of the above
Answer: Option
Explanation:

At 0 K a semiconductor is perfect insulator. At room temperature it is slightly conducting.

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