Q99 / 120 · VITEEE 2008 · Physics

A radio station has two channels. One is AM at $1020 \mathrm{kHz}$ and the other FM at $89.5 \mathrm{MHz}$. For good results you will use

  • Correct answer
    A
    longer antenna for the AM channel and shorter for the FM
  • B
    shorter antenna for the AM channel and longer for the FM
  • C
    same length antenna will work for both
  • D
    information given is not enough to say which one to use for which

Solution

Antenna length $=\frac{\lambda}{4} \propto \lambda$ $\because \lambda \propto \frac{1}{v}$ for cosntant velocity, $\therefore$ Antenna length $\propto \frac{1}{v}$ Here, $v_{\mathrm{AM}} < v_{\mathrm{FM}}$ $\therefore$ Antenna length for AM should be longer than that of FM.

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

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