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If light is considered as wave, then different colored light can be explained as waves of different wavelength/frequency. How colored light can be explained if light is considered as emission of photon?

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The Energy of the Photon defines its frequency. It is the equation $$E=h\nu$$ which puts this in mathematical terms. Where $h$ is Planck's constant, $E$ the Energy and $\nu$ the frequency. This can also be written in terms of wavelength of the photon as $$E=\frac{hc}{\lambda}$$ So blue (high frequency, short wavelength) light has high energy, red (low frequency, large wavelength) has lower energy

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i can't connect waves and particles. aren't photons travel in straight line? if something travels in straight line, how frequency/wavelength can be defined? – Donotalo Aug 25 '11 at 12:19
I'd suggest you read through this Wikipedia article and in case more Questions arise, ask them here – luksen Aug 25 '11 at 12:22
Your followup question is essentially equivalent to "How does quantum physics work?" Needless to say, this is an excellent question, but it's not an easy one to give a quick answer to! – Ted Bunn Aug 25 '11 at 13:45
@Ted Bunn: ok, i'll check them out. thanks. – Donotalo Aug 25 '11 at 16:09

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