In a common emitter transistor amplifier current gain is 9 and resistance gain is 20. The voltage gain will be:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 9 × 20
The voltage gain of an amplifier is the ratio of output voltage to input voltage. Writing each voltage as current times resistance, the voltage gain is the product of the current gain and the resistance gain.
\( \displaystyle A_v = \frac{V_{\mathrm{out}}}{V_{\mathrm{in}}} = \frac{I_{\mathrm{out}}R_{\mathrm{out}}}{I_{\mathrm{in}}R_{\mathrm{in}}} = \frac{I_{\mathrm{out}}}{I_{\mathrm{in}}}\times\frac{R_{\mathrm{out}}}{R_{\mathrm{in}}} \)
\( A_v = 9\times20 = 180 \)
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic was removed from the latest NCERT book (2026-27), and it also appears to be out of the CUET 2026 syllabus.
NCERT (Pre-rationalised edition, 2022-23):
Transistor as a Device – “… We can express the voltage gain AV in terms of the resistors in the circuit and the current gain of the transistor as follows. … So, the voltage gain of this CE amplifier (Fig. 14.32) is given by
\( \displaystyle A_V = -\beta_{ac}\left(R_C / R_B\right) \qquad (14.14) \)”