Semiconductor Electronics

The input resistance of a silicon transistor is 100 . Base current is changed by 40 which results in a change in collector current by 2 mA. This transistor is used as a common emitter amplifier with a load resistance of 4 k . The voltage gain of the amplifier is

1. 2000
2. 3000
3. 4000
4. 1000

Two ideal diodes are connected to a battery as shown in the circuit. The current supplied by the battery is [figure]

1. 0.75 A
2. zero
3. 0.25 A
4. 0.5 A

C and Si both have same lattice structure; having 4 bonding electrons in each. However, C is insulator whereas Si is intrinsic semiconductor. This is because

1. In case of C the valence band is not completely filled at absolute zero temperature.
2. In case of C the conduction band is partly filled even at absolute zero temperature.
3. The four bonding electrons in the case of C lie in the second orbit, whereas in the case of Si they lie in the third.
4. The four bonding electrons in the case of C lie in the third orbit, whereas for Si they lie in the fourth orbit.

The figure shows a logic circuit with two inputs A and B and the output C. The voltage wave forms across A, B and C are as given. The logic circuit gate is [figure]

1. OR gate
2. NOR gate
3. AND gate
4. NAND gate

In a CE transistor amplifier, the audio signal voltage across the collector resistance of 2 k is 2 V. If the base resistance is 1 k and the current amplification of the transistor is 100, the input signal voltage is

1. 0.1 V
2. 1.0 V
3. 1 mV
4. 10 mV

Transfer characteristics [output voltage (V0) vs input voltage (Vi)] for a base biased transistor in CE configuration is as shown in the figure. For using transistor as a switch, it is used [figure]

1. in region III
2. both in region (I) and (III)
3. in region II
4. in region I

A Zener diode, having breakdown voltage equal to 15 V, is used in a voltage regulator circuit shown in figure. The current through the diode is [figure]

1. 5 mA
2. 10 mA
3. 15 mA
4. 20 mA

In the following figure, the diodes which are forward biased, are [figure]

1. (A), (B) and (D)
2. (C) only
3. (C) and (A)
4. (B) and (D)

Pure Si at 500 K has equal number of electron (ne) and hole (nh) concentrations of 1.5 1016 m-3. Doping by indium increases nh to 4.5 1022 m-3. The doped semiconductor is of

1. p-type having electron concentration ne = 5 109 m-3
2. n-type with electron concentration ne = 5 1022 m-3
3. p-type with electron concentration ne = 2.5 1010 m-3
4. n-type with electron concentration ne = 2.5 1023 m-3

In forward biasing of the p-n junction

1. the positive terminal of the battery is connected to p-side and the depletion region becomes thick.
2. the positive terminal of the battery is connected to n-side and the depletion region becomes thin.
3. the positive terminal of the battery is connected to n-side and the depletion region becomes thick.
4. the positive terminal of the battery is connected to p-side and the depletion region becomes thin.