Transistor: Working

Q.

A transistor is operated in a common emitter configuration at $V_C=2V$ such that a change in the base current from 100 $\mu$ A to 300 $\mu$ A produces a change in the collector current from 10 mA to 20 mA. The current gain is

1. 75
2. 100
3. 25
4. 50

Q.

In an NPN transistor circuit, the collector current is 10 mA. If 90% of the electrons emitted reach the collector, the emitter current (i_E) and base current (i_B) are given by

1. 
   

2. 
   

3. 
   

4. 
   

Q. In a common emitter transistor circuit, the base current is $40\mu A$, then $V_{BE}$ is :-

1. $0.2\text{V}$
2. $2\text{V}$
3. $0.8\text{V}$
4. Zero

Q. A transistor is used in common-emitter mode in an amplifier circuit. When a signal of 20 mV is added to the base emitter voltage, the base current changes by 20 $\mu$A and the collector current changes by 2mA. The load resistance is 5k$\Omega$. The trans conductance and the voltage gain are

1. 0.1 mho, 500
2. 0.2 mho, 500
3. 0.3 mho, 1000
4. 0.2 mho, 100

Q.

Can a transistor converts DC to AC?

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.

If a = 0.98 and current through emitter i_e = 20 mA, the value of B(beta) is

1. 96
2. 4.9
3. 9.6
4. 49

Q. If $\alpha$ and $\beta$ are the current gain in the $CB$ and $CE$ configurations respectively of the transistor circuit, then $\frac{\beta -\alpha }{\alpha \beta }$ is equal to

Q. In npn transistor circuit, the collector current is $20\text{mA}$. If $80\text{\%}$ of the electrons emitted reach the collector, the emitter current will be

1. $\text{10 mA}$
2. $\text{15 mA}$
3. $\text{25 mA}$
4. $\text{20 mA}$

Q.

A transistor is used in common emitter mode as an amplifier. Then:

Q. (a) Draw the circuit diagram of an n-p-n transistor amplifer in common emitter configuration.
(b) Derive an experssion for voltage gain of the amplifier and hence show that the output voltage is in opposite phase with the input voltage.

Q. The diagram shows the biasing of an n-p-n transistor in common emitter configuration used in an amplifier. The design of the transistor is such that $98\%$ of the charge carriers from emitter reach the collector. If base current changes from $50\mu A$ to $100\mu A$, then the corresponding change in the voltage across the load resistance $R_L$ will be

1. $0.25V$
2. $24.5V$
3. $49.0V$
4. $0.25V$

Q. Consider following two statements

$\left(A\right)$ In forward biased condition, width of depletion region in p-n junction diode decreases.

$\left(B\right)$ Barrier potential of a p-n junction depends on amount of doping.

The correct statement(s) is/are

1. Only $\left(A\right)$
2. Only $\left(B\right)$
3. Both $\left(A\right)$ and $\left(B\right)$
4. Neither $\left(A\right)$ nor $\left(B\right)$

Q.

Do all the electrons that absorb a photon come out as photoelectrons?

Q.

In a series resonant circuit the ac voltages across R, inductance L and capacitance C are 5V, 10 V and 10V respectively. The ac voltage applied to the circuit will be:

1. 10 V

2. 20 V

3. 5 V

4. 25 V

Q. In an AC circuit the applied potential difference and the current flowing are given by:
V = 200 sin 100 t volt,
I = 5 sin $[100t+\frac{\pi }{2}]amp$
The average power consumed in the circuit is

1. 1000 W
2. 40 W
3. 20 W
4. zero

Q.

How do you remember PNP and NPN?

Q.

What is the difference between transistors and thyristors?

Q. A) If a proton had a radius $R$ and the charge was uniformly distributed, calculate using Bohr theory, the ground state energy of a $H-atom$ when $R=0.1\stackrel{o}{A}$.

B) If a proton had a radius $R$ and the charge was uniformly distributed, calculate using Bohr theory, the ground state energy of a $H-atom$ when $R=10\stackrel{o}{A}$.

Q.

Do the Transistors have polarity ?

Q.

Which bias condition produces majority carrier current?

Q. Which is not the correct relation between different current gain $(\alpha ,\beta ,\gamma )$ of transistor amplifier :-

1. $\beta =\frac{\alpha }{1-\alpha }$
2. $\alpha =\frac{\beta }{\beta +1}$
3. $\beta =\gamma +1$
4. $\alpha =\frac{\beta }{\gamma }$

Q.

When transistors are used in digital circuits they usually operate in the

Q.

Can transistors amplify AC signals?

Q. In a common -base amplifier, the phase difference between the input signal voltage and output voltage is :

1. $0$
2. $\frac{\pi }{4}$
3. $\pi$
4. $\frac{\pi }{2}$

Q. Define $\alpha$ and $\beta$ for a transistor. Derive relation between them. In a $CE$ transistor circuit if $\beta =100$ and $I_B=50\mu A$. Compute the values of $\alpha ,I_E$ and $I_C$.

Q.

What does a transistor amplify?

Q. For the transistor circuit shown in figure. Find the value of $R_B\left(\text{in}k\Omega \right)$ nearly is (integer only).
[If $I_C=1\text{mA},V_{CE}=3\text{V},V_{BE}=0.5\text{V},V_{CC}=12\text{V}$ and $\beta =100$]

Q.

What is a BJT?

Q. An electron emitted by a heated cathode and accelerated through a potential difference of $2\text{kV}$ enters a region with uniform magnetic field of $0.15\text{T}$. If the magnetic field makes an angle of ${30}^{\circ }$ with the initial velocity, the radius of the hellical trajectory of electron will be: $(m_e=9.0\times {10}^{-31}\text{kg})$

1. $0.5\text{mm}$
2. $1.5\text{mm}$
3. $2.5\text{mm}$
4. $1\text{mm}$