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Transistor as an amplifier
Appears in
Concepts tested here
- Voltage gain of CE amplifier 2
- Phase reversal in CE amplifier
- Voltage gain and power gain
- Voltage gain and transconductance
All Questions
2015 AIPMT-II 1 question
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The input signal given to a CE amplifier having a voltage gain of 150 is $V_i = 2\cos\left(15t + \frac{\pi}{3}\right)$. The corresponding output signal will beA CE amplifier introduces a phase difference of $\pi$ between input and output.
$V_0 = A_vV_{in} = 150\times 2\cos\left(15t + \frac{\pi}{3} + \pi\right)$
$V_0 = 300\cos\left(15t + \frac{4\pi}{3}\right)$
2013 NEET 1 question
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In a common emitter (CE) amplifier having a voltage gain G, the transistor used has transconductance 0.03 mho and current gain 25. If the above transistor is replaced with another one with transconductance 0.02 mho and current gain 20, the voltage gain will be:Voltage gain $A_V = \frac{\Delta V_C}{\Delta V_B} = \frac{R_L\Delta I_C}{\Delta V_B} = g_mR_L$
$\frac{A_{V_1}}{A_{V_2}} = \frac{g_{m_1}}{g_{m_2}} \Rightarrow \frac{G}{A_{V_2}} = \frac{0.03}{0.02}$
$A_{V_2} = \frac{2}{3}G$
2012 AIPMT-MAINS 1 question
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The input resistance of a silicon transistor is 100 $\Omega$. Base current is changed by 40 $\mu$A, 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$\Omega$. The voltage gain of the amplifier is$R_i = 100\ \Omega$, $\Delta i_B = 40\times10^{-6}$ A, $\Delta i_C = 2\times10^{-3}$ A, $R_o = 4\times10^3\ \Omega$
Current gain $\beta = \frac{\Delta i_C}{\Delta i_B} = \frac{2\times10^{-3}}{40\times10^{-6}} = 50$
$A_V = \beta\frac{R_o}{R_i} = \frac{R_o\times\Delta i_C}{R_i\times\Delta i_B} = \frac{4\times10^3\times2\times10^{-3}}{100\times40\times10^{-6}}$
$A_V = 2000$
2012 AIPMT-PRE 1 question
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In a CE transistor amplifier, the audio signal voltage across the collector resistance of 2 k$\Omega$ is 2 V. If the base resistance is 1 k$\Omega$ and the current amplification of the transistor is 100, the input signal voltage isVoltage gain $A_V = \frac{V_o}{V_i} = \beta\frac{R_C}{R_B}$
$\frac{2}{V_i} = 100\times\frac{2\times10^3}{1\times10^3} = 200$
$V_i = \frac{2}{200} = 0.01$ V = 10 mV
2010 AIPMT-PRE 1 question
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A common emitter amplifier has a voltage gain of 50, an input impedance of 100 $\Omega$ and an output impedance of 200 $\Omega$. The power gain of the amplifier isVoltage gain of a CE amplifier: $A_V = \beta\frac{R_{out}}{R_{in}}$, where $\beta = \frac{I_C}{I_B}$ is the current gain.
$50 = \beta\times\frac{200}{100}$
$\beta = \frac{50\times100}{200} = 25$
Power gain = voltage gain × current gain = $A_V\times\beta$
Power gain = $50\times25 = 1250$