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Question: Answered & Verified by Expert
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
PhysicsCurrent ElectricityVITEEEVITEEE 2008
Options:
  • 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:
2342 Upvotes Verified Answer
The correct answer is: longer antenna for the AM channel and shorter for the FM
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.

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