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# What is the frequency of light having a wavelength of 405 nm?

### 4 Answers

- skipperLv 71 decade agoFavorite Answer
I find it easiest to memorize one equation, and then rearrange it if required-

wavelength = c / frequency

rearranging-

frequency = c/wavelength

c = 3.00 x 10^8 m s^-1

wavelength = 405x10^-9 m = 4.05 x 10^-7 m

frequency = 3.00x10^8 / 4.05x10^-7 = 7.41x10^14 s^-1

frequency = 7.41x10^14 Hz

- Anonymous5 years ago
Use the vacuum wavelengths to get the frequencies: f1 = c / lambda1 f2 = c / lambda2 In a dispersive medium, the frequency doesn't change, but the speed and wavelength do. So the speed is proportional to the wavelength. For each frequency, the speed is: v = c (lambda in medium / lambda in vacuum) And hence the index of refraction is: n = c/v = lambda in vacuum / lambda in medium If you want index (and hence speed) as a function of wavelength, with two points, you could fit the first two terms of the cauchy equation: n(lambda) = A + B / lambda^2 + ....

- 1 decade ago
Wave velocity = frequency

wavelength

299,792,458 m/s = 740228291358024 /second = 740 x 1012 Hz = 740 TeraHertz

405 x 10-9 m

300,000,000 m/s is often used as an approximate wave velocity rather than 299,792,458.