MediumChemistryHigh School (11–12)Structure of the Atom › Light, Atomic Spectra and the Bohr ModelNumerical

A green laser pointer has a power of 5.0 mW and a wavelength of 532 nm.

Try it on paper first. A hint, the key idea and the worked solution are here when you need them.

A green laser pointer has a power of $5.0\ \text{mW}$ and a wavelength of $532\ \text{nm}$ . Find the energy of one photon, and the number of photons that leave the pointer every second.

Need a reminder? The key ideaShow

A photon carries $E = h\nu = \dfrac{hc}{\lambda}$ , with $h = 6.626 \times 10^{-34}\ \text{J s}$ ; in eV, $E = \dfrac{1240}{\lambda\ (\text{nm})}$ . Photoelectric effect: $h\nu = W + KE_{\max}$ , and $eV_0 = KE_{\max}$ . Brightness sets the number of electrons; frequency sets their energy.

The worked solution

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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.

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