EasyPhysicsHigh School (11–12)Modern Physics › Dual Nature of Radiation and Matter Quantum MechanicsNumericalBoard Exam AP A-Level IB

A metal has a work function of 2.75 eV. Ultraviolet light of 350 nm falls on it…

Contributed by Arnie

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

A metal has a work function of $2.75\ \text{eV}$ . Ultraviolet light of $350\ \text{nm}$ falls on it. Find the largest kinetic energy of the electrons and the stopping potential. Use $hc = 1240\ \text{eV nm}$ .

Need a reminder? The key ideaShow

A photon has $E = h\nu = \dfrac{hc}{\lambda}$ , with $hc = 1240\ \text{eV nm}$ . Einstein: $KE_{\max} = h\nu - \phi$ , and $eV_0 = KE_{\max}$ . No electrons leave below the threshold, $h\nu_0 = \phi$ . Brightness changes the number of electrons, not 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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