# physics

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A typical smaall laser has a power of 0.5mW= 5*10^-4J/s. How many photons are emitted each second by the laser?

• physics -

Power = (photons/sec)*(energy per photon)

To get an answer, you need to know what the wavelength (or frequency) is. This is what determines the photon energy.

Most, but not all, small lasers are red, so you could assume a wavelength of 630*10^-9 m. That would make the photon
3.1*10^-19 J.

Photons/s = (5*10^-4 J/s)/(3.1*10^-19 J)
= ______

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