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For a 10 MHz radio wave to be reflected by the ionosphere in sky-wave communication, what is the least electron density required in the ionospheric layer?

1. About 1.2 × 10¹² m⁻³
2. About 10⁶ m⁻³
3. About 10¹⁴ m⁻³
4. About 10²² m⁻³

Correct answer: About 1.2 × 10¹² m⁻³

Solution

The correct option is right because the minimum electron density required for reflecting a 10 MHz radio wave is approximately 1.2 × 10¹² m⁻³, which allows the wave to encounter sufficient free electrons to reflect back to the Earth's surface, enabling effective sky-wave communication.

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