JEE Main & Advanced Physics Semiconducting Devices Question Bank Critical Thinking

  • question_answer
    For a triode m = 64 and gm =1600 m mho. It is used as an amplifier and an input signal of 1V (rms) is applied. The signal power in the load of 40 kW will be

    A)            23.5 mW                                

    B)            48.7 mW

    C)            25.6 mW                                

    D)            None of these

    Correct Answer: C

    Solution :

                       \[{{r}_{p}}=\frac{\mu }{{{g}_{m}}}=\frac{64}{1600\times {{10}^{-6}}}=4\times {{10}^{4}}\Omega \] Voltage gain \[{{A}_{v}}=\frac{\mu }{1+\frac{{{r}_{p}}}{{{R}_{L}}}}=\frac{64}{1+\frac{4\times {{10}^{4}}}{40\times {{10}^{3}}}}=32\] \ Output signal voltage \[{{V}_{0}}={{A}_{v}}\times {{V}_{i}}=32\times 1=32\,V\,(r.m.s.)\] Signal power in load \[=\frac{V_{0}^{2}}{{{R}_{L}}}=\frac{{{(32)}^{2}}}{40\times {{10}^{3}}}=25.6\,mW\]


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