Q135 / 180 · AIIMS 2018 (27 May) · Physics

If the modulation index of an amplitude modulated wave is changed from 0 to 1 , then the transmitted power will be

  • A
    unchanged
  • B
    doubled
  • Correct answer
    C
    increased by $50 \%$
  • D
    zero

Solution

The transmitted power in AM wave is $P_t=\left(1+\frac{\mu^2}{2}\right) P_c$ where $\mu$ is the modulation index and $P_c$ is the power in carrier wave. When $\mu=0, P_t=P_c$ and when $\mu=1, P_t=\left(1+\frac{1}{2}\right) P_c=\frac{3}{2} P_c$ $\therefore$ The percentage increase in transmitted power $=\frac{\frac{3}{2} P_c-P_c}{P_c} \times 100 \%=\frac{1}{2} \times 100 \%=50 \%$

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

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