Important Questions For Practice
1. What is the function of base region of a transistor? Why is this region made thin and lightly doped? Draw a circuit diagram to study the input and output characteristics of n-p-n transistor in a common emitter configuration. Show these characteristics graphically.
2. In an n-p-n transistor circuit, the collector current is 10mA. If 90% of the electrons emitted reach the collector, find the base current and emitter current.
3. A p-n junction is fabricated from a semiconductor with a band gap of 2.8 eV. Can it detect a wavelength of 600 nm? Justify your answer.
4. A carrier wave of peak voltage 12v is used to transmit a message signal. What should be the peak voltage of the modulating signal in order to have a modulation index of 75%?
5. If the current gain of a CE тАУ Amplifier is 98 and collector current Ic = 4 mA, determine the base current.
Questions From Board Papers
1. Semiconductors do not support strong current i.e., a semiconductor is damaged when strong current passes through it. Why?
2. Name the semiconductor device that can be used to regulate an unregulated dc power supply.
3. A semiconductor device is connected in a series circuit with a battery and a resistance. A current is found to pass through the circuit. When polarity of the battery is reversed, the current drops to almost zero. Name the semiconductor device.
4. The output of a 2 input AND gate is fed as input to a NOT gate. Write the truth table for the final output of the combination. Name this new logic gate formed.
5. Which special type of diode can act as a voltage regulator? Give the symbol of this diode and draw the general shape of its V-I characteristics.
Important Questions On 12th Physics Chapter 14
For a half-wave rectifier, the output frequency is equal to the input frequency.
Output frequency = 50 Hz
For a full-wave rectifier, the output frequency is twice the input frequency.
Output frequency = 2 ├Ч 50 = 100 Hz
Voltage gain of the second amplifier, V2 = 20
Input signal voltage, Vi = 0.01 V
Output AC signal voltage = Vo
The total voltage gain of a two-stage cascaded amplifier is given by the product of voltage gains of both the stages, i.e.,
V = V1 ├Ч V2 = 10 ├Ч 20 = 200
We have the relation:
Vo = V ├Ч Vi = 200 ├Ч 0.01 = 2 V
Therefore, the output AC signal of the given amplifier is 2 V.