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AM radio waves cannot travel freely out through the atmosphere. What stops them?
AThe ionosphere
BThe ozone layer
CThe magnetic field
DThe clouds of dust
Answer & Solution
Correct answer: A. The ionosphere
1. Different radio wavelengths meet the atmosphere in different ways.
2. FM and TV waves pass straight through it.
3. AM waves are absorbed or reflected by the ionosphere, a layer of charged particles high up.
4. The ozone layer stops ultraviolet rays instead, so it is the wrong barrier here.
_Source: OpenStax Astronomy (CC BY 4.0), Ch 4 "Earth, Moon, and Sky" and Ch 5 "Radiation and Spectra", section 5.2 The Electromagnetic Spectrum_
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