You are listening to AM radio in a car driving west from downtown Portland on Bu

Question

You are listening to AM radio in a car driving west from downtown Portland on Burnside. Near the city limits, you enter a tunnel and lose AM-band radio reception. While still in the tunnel, you switch the radio to the FM-band and are able to receive and FM-band signal. Using concepts discussed in class, explain the above observation using about 40 words or less Why is it that you can hear the FM-band station but not the AM-band station when you are in the tunnel? Do a simple calculation to justify your explanation. (For simplicity, assume that the AM station is broadcasting at 1000 kHz while the FM station broadcasts at 100 MHz.)

Explanation / Answer

Think:Electromagnetic waves of low frequency will face troubles in passing through metal gaps while those of high frequency will pass easily through metal gaps.

Given info : FAM = 1000 kHz and FFM = 100 MHz

The units for the numbers on the AM are in kHz, and the units for the numbers on the FM are in MHz. An AM radio station operates at 1000 kHz, or 1000,000 cycles per second. An FM station operates at 100 MHz, or 100,000,000 cycles per second.While we observe that both these frequencies are incredibly huge , FFM >>>> FAM and thus when you travel inside a tunnel, the 1000 kHz signal fades and 100 MHz signal stays with you. The FM signal is a high enough so that it can pass through the gaps in the metal mesh that supports the tunnel while the AM signal is blocked by this mesh.

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