Considering a 1 dimensional problem:(adsbygoogle = window.adsbygoogle || []).push({});

If I'm not wrong, in case of having 2 monochromatic plane waves such that [tex]E_1=E_{01} \cos (k_1 x - \omega _1 t)[/tex] and [tex]E_2=E_{01} \cos (k_2 x - \omega _2 t)[/tex] (so the same intensity but different wavelength), if we sum them up we reach another wave: [tex]E=2E_{01} \cos \left ( \frac{(k_1+k_2)x - (\omega _1 + \omega _2)t}{2} \right ) \cdot \cos \left ( \frac{(k_1-k_2)x - (\omega _1 -\omega _2)t}{2} \right )[/tex]. I've asked at my university if I choose the waves as being in the visible spectra if the resulting wave would be in the visible spectra. I've also asked that in case of an affirmative answer, why when we sum up all the waves (infinitely of them, but a big number is a good approximation I guess) forming the visible spectra, we get a "white color" while white hasn't even a defined wavelength.

Now I realize that if you mix paints like yellow and blue, your eyes will see "green" but I believe that any instrument could show that the light is composed of yellow and green. While I do not think any instrument could tell whether the light coming from 2 very very close Red+Green lasers is composed or not. I might be plain wrong, I'm just guessing here.

Anyway, my biggest worry isto know whether the resulting wave has a proper wavelength, thus "color". I've been told that no. But I can't grasp it mentally, I mean it's the sum of 2 waves that have a proper wavelength. So although the resulting wave might look ugly, it must repeat itself over time... right? And so having a wavelength?

I'm a bit confused about this. Any enlightenment is very welcome.

Another question: Can sunlight on Earth be considered as a coherent light? I think we can consider the rays as being parallel.

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# Light as a wave, frequency question

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