Introduction to Transistor

Q. The threshold frequency for a certain metal is $3.3\times {10}^{14}\text{Hz}$. If light of frequency $8.2\times {10}^{14}\text{Hz}$ is incident on the metal, predict the cut - off voltage for the photoelectric emission.

Q. What is the function of choke

Q.

For a transistor, the current amplification factor(α) is 0.8. The transistor is connected in common emitter configuration. The change in collector current, when the base current changes by 6 mA is

1. 24 mA

2. 6 mA

3. 4.8 mA

4. 8 mA

Q.

An LC circuit contains a 20 mH inductor and a 50 μF capacitor with an initial charge of 10 mC. The resistance of the circuit is negligible. Let the instant the circuit is closed be t = 0.

(a) What is the total energy stored initially? Is it conserved during LC oscillations?

(b) What is the natural frequency of the circuit?

(c) At what time is the energy stored

(i) completely electrical (i.e., stored in the capacitor)? (ii) completely magnetic (i.e., stored in the inductor)?

(d) At what times is the total energy shared equally between the inductor and the capacitor?

(e) If a resistor is inserted in the circuit, how much energy is eventually dissipated as heat?

Q.

For transistor action, which of the following statements are correct:

(a) Base, emitter and collector regions should have similar size and doping concentrations.

(b) The base region must be very thin and lightly doped.

(c) The emitter junction is forward biased and collector junction is reverse biased.

(d) Both the emitter junction as well as the collector junction are forward biased.

Q. To be in active state, emitter-base junction of a transistor is _______ biased while the collector-base junction is ________.

1. reverse, reverse
2. forward, forward
3. forward, reverse
4. reverse, forward

Q.

What are the types of sinusoidal oscillator?

Q.

A common emitter amplifier is designed with n-p-n transistor (α =0.99). The input impedance is 1 KΩ and the load is 10 KΩ. The voltage gain will be.

1. 99

2. 9.9

3. 990

4. 9900

Q.

In a common base transistor circuit, the current gain is 0.98. On changing emitter current by 5 mA, the change in collector current is

1. 2.45 mA

2. 0.196 mA

3. 4.9 mA

4. 5.1 mA

Q.

To use a transistor as an amplifier:

1. No bias voltage is required.

2. Both junctions are forward biased

3. Both junctions are reverse biased.

4. The emitter-base junction is forward biased and the base-collector junction is reverse biased.

Q. The most commonly used transistor arrangement is .

1. common emitter
2. common base
3. common collector

Q. In which of the following situations, the transistor is operating in the active region ?

1. 
2. 
3. 
4. 

Q. Draw a circuit diagram of n-p-n transistor amplifier in CE configuration. Under what condition does the transistor act as an amplifier?

Q. The positive feedback is required by an amplifier to act as an oscillator. The feedback here means:

Q.

Do capacitors convert AC to DC?

Q.

State two multiples and two submultiples of the unit of electrical potential and electric current.

Q.

The transistor provides good power amplification when they are used in___.

Q. An isolated capacitor has charge \(Q\) and plate area \(A\). Between the plates of a parallel plate condenser, a plate of thickness \(t_1\) and dielectric constant \(k_1\) is placed. In the rest of the space, there is another plate of thickness \(t_2\) and dielectric constant \(k_2\) . The potential difference across the condenser will be

Q.

What is electrical resonance? Give one example.

Q.

Express the heat produced in calories, when I amperes are passed for t seconds through a resistor having the resistance of R ohms.

Q.

In a common emitter transistor, the current gain is 80. What is the change in collector current, when the change in base current is 250 mA

1. (250 - 80) mA
2. (250 + 80) mA

3. 80 ´ 250 mA

4. 250/80 mA

Q. What are the important characteristics of an Operational Amplifier (OP-AMP)?

Q. The capacitors in the figure are initially uncharged and are connected as in the diagram with switch $S$ open. The potential of point b after switch $S$ is closed and the amount of charge that flowed through the switch when it was closed are

1. $66.7V,300\mu C$
2. $100V,400\mu C$
3. $100V,300\mu C$
4. $133.3V,0\mu C$

Q.

Where is PNP transistor used?

Q.

The input voltage applied to a cascaded amplifier (consisting of two amplifiers) is 0.02 V and the output voltage is 6 V. The voltage gain of one of the two amplifiers is 10. What is the voltage gain of the other amplifier?

1. 1/30

2. 1/3

3. 30

4. 3

Q. The most commonly used transistor arrangement is .

1. common emitter
2. common base
3. common collector

Q. Consider the LCR circuit shown in figure.
Find the net current $i$ and the phase of $i$.
Show that $i=\frac{W}{z}.$ Find the impendance $Z$ for this circuit.

Q. A) You are given the circuit as shown in figure. Show that circuit acts as OR gate.

B) You are given the circuit as shown in figure. Show that circuit acts as AND gate.

Q. In the $LCR$ circuit shown in figure, the AC driving voltage is $v=v_{m}sin\omega t.$


A) Write down the equation of motion for q(t).

B) At $t=t_0,$ the voltage source stops, and $R$ is short circuited. Now write down how much energy is stored in each of $L$ and $C$.

C) Describe subsequent motion of charges.

Q.

How to find the direction of the induced current?