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An electromagnetic radiation has a wavelength comparable to the length of a football field (of the order of 100 m). Which part of the spectrum does it belong to?

1. Microwave
2. Gamma ray
3. Radio wave
4. X-ray

Correct answer: Radio wave

Solution

A wavelength of about 100 m gives a frequency f = c/lambda = 3x10⁸ / 100 = 3 MHz, which lies firmly in the radio-wave band. Microwaves are cm-scale, X-rays and gamma rays are far shorter.

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