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What is the frequency of a radio wave with a wavelength of 3 km?
  • A
    100 MHz
  • B
    300 MHz
  • C
    100 kHz
  • D
    300 kHz

Refer to figure.

For this question, using the standard formulae, first there needs to be a conversion made.
From km to m. 3 km corresponds to 3000 m.

Use the simplified standard formulae:
λ (in meters) = (c (300))/(f (in MHz))

Known is the speed of light (c) and the wavelength (λ).
Rearranging the formulae gives the following:
F (in MHz) = (c (300))/(λ (in meters)) = 300/(3000) = 0,1MHz.

Using the figure, 0,1 MHz converts to 100 kHz.

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