We’re being asked **how many photons per second** are being emitted by a red laser with a wavelength of **630 nm** with a power of **2.50 watts**.

Recall that the ** energy of a photon (E)** is given by:

$\overline{){\mathbf{E}}{\mathbf{=}}{\mathbf{hv}}}\left(1\right)$

where:

**h** = Planck’s constant (6.626 × 10^{–34} J • s)

**v** = frequency (in s^{–1})

Also, recall that the frequency (v) and wavelength (λ) are related:

$\overline{){\mathbf{\lambda}}{\mathbf{=}}\frac{\mathbf{c}}{\mathbf{v}}}\left(2\right)$

where:

**c** = speed of light (3.0 × 10^{8} m/s)

The power of a red laser (λ = 630 nm) is 2.50 watts (abbreviated W, where 1 W = 1 J/s). How many photons per second does the laser emit?

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Based on our data, we think this problem is relevant for Professor Habel Rodriguez's class at UNM.