Semiconductor Electronics · Question 85

A transistor is operated in common emitter configuration at constant collector voltage VC = 1.5 V such that a change in the base current from 100 to 150 produces a change in the collector current from 5 mA to 10 mA. The current gain is

1. 50
2. 67
3. 75
4. 100

Choose the only false statement from the following.

1. In conductors the valence and conduction bands overlap.
2. Substances with energy gap of the order of 10 eV are insulators.
3. The resistivity of a semiconductor increases with increase in temperature.
4. The conductivity of a semiconductor increases with increase in temperature.

Zener diode is used for

1. amplification
2. rectification
3. stabilisation
4. producing oscillations in an oscillator.

Application of a forward bias to a p-n junction

1. widens the depletion zone
2. increases the potential difference across the depletion zone
3. increases the number of donors on the n side
4. decreases the electric field in the depletion zone.

Carbon, silicon and germanium atoms have four valence electrons each. Their valence and conduction bands are separated by energy band gaps represented by (Eg)C, (Eg)Si and (Eg)Ge respectively. Which one of the following relationships is true in their case?

1. (Eg)C > (Eg)Si
2. (Eg)C < (Eg)Si
3. (Eg)C = (Eg)Si
4. (Eg)C < (Eg)Ge.

In a p-n junction photo cell, the value of the photo-electromotive force produced by monochromatic light is proportional to

1. The barrier voltage at the p-n junction.
2. The intensity of the light falling on the cell.
3. The frequency of the light falling on the cell.
4. The voltage applied at the p-n junction.

In semiconductors at room temperature

1. the valence band is partially empty and the conduction band is partially filled
2. the valence band is completely filled and the conduction band is partially filled
3. the valence band is completely filled
4. the conduction band is completely empty

The peak voltage in the output of a half wave diode rectifier fed with a sinusoidal signal without filter is 10 V. The d.c. component of the output voltage is

1. (10/ 2) V
2. ( 10 ) V
3. 10 V
4. (20/ ) V

The output of OR gate is 1

1. if both inputs are zero
2. if either or both inputs are 1
3. only if both inputs are 1
4. if either input is zero

Of the diodes shown in the following diagrams, which one is reverse biased?

1. [figure]
2. [figure]
3. [figure]
4. [figure]