Q133 / 180 · AIIMS 2009 · Physics

Assertion : In a common-emitter amplfier, the load resistance of the output circuit is 1000 times the load resistance of the input circuit. If $\alpha=0.98$, then voltage gain is $49 \times 10^3$. Reason : $\alpha=\frac{\beta}{1-\beta}$ (symbols have their usual meaning).

  • A
    If both assertion and reason are true and reason is the correct explanation of assertion
  • B
    If both assertion and reason are true but reason is not the correct explanation of assertion
  • Correct answer
    C
    If assertion is true but reason is false
  • D
    If both assertion and reason are false.

Solution

We know that $\alpha=\frac{\Delta i_C}{\Delta i_E}$ and $\beta=\frac{\Delta i_C}{\Delta i_B}$ Also $\beta=\frac{\alpha}{1-\alpha}=\frac{0.98}{1-0.98}=49$ $\therefore$ Voltage gain $=\beta=\frac{R_2}{R_1}=49 \times 1000=49 \times 10^3$

Hence, the correct answer is option: 'C'.

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