Transistor as an Amplifier

Q. For a CE-transistor amplifier, the audio signal voltage across the collector resistance of 2 k$\Omega$ is 2 V. Suppose the current amplification factor of the transistor is 100, find the input signal voltage and base current, if the base resistance is 1 k$\Omega$.

Q. A npn transistor is connected in common emitter configuration in a given amplifier. A load resistance of $800\Omega$ is connected in the collector circuit and the voltage drop across it is 0.8V. If the current amplification factor is 0.96 and the input resistance of the circuit is $192\Omega$, the voltage gain and the power gain of the amplifier will respectively be:

1. 4, 3.84
2. 4, 4
3. 4, 3.69
4. 3.69, 3.84

Q. A transistor is connected in common emitter circuit configuration, the collector supply voltage is $10\text{V}$ and the voltage drop across a resistor of $1000\Omega$ in the collector circuit is $0.6\text{V}$. If the current gain factor $\left(\beta \right)$ is $24$, then the base current is _____ $\mu \text{A}$.
(Round off to the Nearest Integer)

Q. The current flowing through the Zener diode in the figure is

1. $20\text{mA}$
2. $10\text{mA}$
3. $15\text{mA}$
4. $5\text{mA}$

Q. Current gain ${\beta }_{AC}$ in common emitter mode of transistor is

1. 
2. 
3. 
4. 

Q.

What Is Amplifier?

Q. The transfer ratio of a transistor is 50. The input resistance of the transistor when used in the common-emitter configuration is 1 kΩ. The peak value of the collector AC current for an AC input voltage of 0.01 $V$ peak is (in $\mu m$)

Q. A common emitter amplifier circuit, built using an $\text{npn}$ transistor, is shown in the figure. Its dc current gain is $250,R_C=1\text{k}\Omega$ and $V_{CC}=10\text{V}$. What is the minimum base current for $V_{\text{CE}}$ to reach saturation ?

1. $40\mu \text{A}$
2. $100\mu \text{A}$
3. $10\mu \text{A}$
4. $7\mu \text{A}$

Q. A transistor is used in common-emitter mode in an amplifier circuit. When a signal of $10\text{mV}$ is added to the base-emitter voltage, the base current changes by $10\mu A$ and the collector current changes by $1.5\text{mA}$. The load resistance is $5k\Omega$. The voltage gain of the transistor will be

Q. A voltmeter has a resistance of $G$ $\Omega$ and range $V\text{volt}$. The value of resistance used in series to convert it into voltmeter of range $nV\text{volt}$ is

1. $nG$
2. $(n-1)$$G$
3. $\frac{G}{n}$
4. $\frac{G}{n-1}$

Q. In common emitter amplifier, the current gain is $20.$ The collector resistance and input resistance are $4k\Omega$ and $800\Omega$ respectively. If the input voltage is $0.01\text{V}.$ The output voltage is

1. $0.01\text{V}$
2. $1\text{V}$
3. $100\text{V}$
4. $200\text{V}$

Q.

An amplifier has a voltage gain $A_v=1000$. The voltage gain in $dB$ is

1. $30dB$

2. $60dB$

3. $3dB$

4. $20dB$

Q. Current gain of a transistor in common base mode is 0.95. Its value in common emitter mode is

1. 1.5
2. 0.95
3. 19
4. (19)^–1

Q. One way in which the operation of an $\text{n-p-n}$ transistor differ from that of a $\text{p-n-p}$ transistor is that

1. the emitter junction is reverse biased in $\text{n-p-n}$.
2. the emitter junction injects minority carriers into the base region of $\text{p-n-p}$.
3. the emitter injects holes into the base of the $\text{p-n-p}$ and electrons into the base region of $\text{n-p-n}$.
4. the emitter injects holes into the base of $\text{n-p-n}$.

Q. In common emitter amplifier, the current gain is $62$. The collector resistance and input resistance are $5\text{k}\Omega$ and $500\Omega$ respectively. If the input voltage is $0.01\text{V}$, the output voltage will be

1. $0.62\text{V}$
2. $6.2\text{V}$
3. $62\text{V}$
4. $620\text{V}$

Q.

When the base current in a transistor is changed from $30\mu A$ to $80\mu A,$ the collector current is changed from 1.0 mA to 3.5 mA. Find the current gain $\beta .$

Q.

In a common emitter amplifier circuit using an NPN transistor, the phase difference between the input and the output voltages will be:

1. $45°$

2. $90°$

3. $135°$

4. $180°$

Q. A Zener diode is connected to a battery and a load as shown below. The currents $I,I_z$ and $I_L$ are respectively

1. $12.5\text{mA},5\text{mA},7.5\text{mA}$
2. $15\text{mA},7.5\text{mA},7.5\text{mA}$
3. $15\text{mA},5\text{mA},10\text{mA}$
4. $12.5\text{mA},7.5\text{mA},5\text{mA}$

Q. What is the emitter current if $I_B=20\mu A$ and $\beta =100$ ?

1. $2.02mA$
2. $1.01mA$
3. $2.00mA$
4. $120mA$

Q. Consider an electrical circuit containing a two way switch ${}^{\prime }{S}^{\prime }$. Initially $S$ is open and then $T_1$ is connected to $T_2$. As the current in $R=6\Omega$ attains a maximum value of steady state level, $T_1$ is disconnected from $T_2$ and immediately connected to $T_3$. Potential drop across $r=3\Omega$ resistor immediately after $T_1$ is connected to $T_3$ is _____ $\text{V}$.
(Round off to the Nearest Integer)

Q. Draw a typical output characteristics of an $n-p-n$ transistor in a $CE$ configuration. Show how these characteristics can be used to determine output resistance.

Q. Current gain in common base configuration is less than 1 because

1. I_e < I_b
2. I_b < I_e
3. I_c < I_e
4. I_e < I_c

Q. For a transistor amplifier, the voltage gain (a) remains constant for all frequencies. (b) is high at high and low frequencies and constant in the middle frequency range. (c) is low at high and low frequencies and constant at mid frequencies. (d) None of the above.

Q. A $\text{PNP}$ in common emitter configuration used as an amplifier, its current gain is $50$. If input resistance is $1k\Omega$ and input voltage is $5\text{V}$ , then output current will be-

1. $250\text{mA}$
2. $30\text{mA}$
3. $50\text{mA}$
4. $100\text{mA}$

Q.

The voltage gain of an amplifier with $9\%$ negative feedback is $10$. The voltage gain without feedback will be:

1. $100$

2. $90$

3. $1.25$

4. $10$

Q. A signal of $20\text{mV}$ is applied to common emitter transistor amplifier circuit. Due to this, the change in base current and the change in collector current are $20\mu \text{A}$ and $2\mu \text{A}$ respectively. The load resistance is $10\text{k}\Omega$. The voltage gain is,

1. $1000$
2. $100$
3. $10$
4. $0.01$

Q. In a series $LCR$ circuit, $R=200\Omega$ and the voltage and the frequency of the main supply is $220\text{V}$ and $50\text{Hz}$ respectively. On taking out the capacitance from the circuit, the current lags behind the voltage by ${30}^{\circ }$. On taking out the inductor from the circuit, the current leads the voltage by ${30}^{\circ }$. The power dissipated in the $LCR$ circuit is-

1. $305\text{W}$
2. $210\text{W}$
3. $0\text{W}$
4. $242\text{W}$

Q. A circuit element shown in the figure contains a box is having either a capacitor or an inductor. The power factor of the circuit is $0.8$, while current lags behind the voltage. Find the value of $\frac{V}{100}$ where $V\text{volts}$ is the source voltage. Assume box element to be ideal.

Q. In the given circuit, the potential difference across the capacitor is $10\text{V}$. Each resistance is $3\Omega$. The cell is ideal. The emf of the cell is

1. $14\text{V}$
2. $16\text{V}$
3. $18\text{V}$
4. $24\text{V}$

Q. For a common emitter amplifier, current gain is 50. What is the current gain if it is working as common base amplifier?

1. 1.02
2. 0.98
3. 98
4. 1