Physics electromagnetic waves?

Question

Light visible to humans consists of electromagnetic waves with wavelengths (in air) in the range 400-700 nm (4.0 10-7 m - 7.0 10-7 m). The speed of light in air is 3.0 108 m/s. What are the frequencies of electromagnetic waves that are visible?

1.) 4.1 e14 to 7.7 e14 Hz

2.) 4.0 e14 to 7.1 e 14 Hz

3.) 4.3 e14 to 7.5 e 14 Hz

4.) 4.5 e 14 to 7.9 e 14 Hz

Answer 1

The frequency of an e.m. wave is its speed divided by its wavelength.

f=3* (10^8)/ (400*10^-9)=4.5 * 10^14 Hz

f'=3 *(10^8)/ (700*10^-9)=4.3* 10^14 Hz

Answer 3 is correct.

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