A metal exposed to light of wavelength $800 \mathrm{~nm}$ and and emits photoelectrons with a certain kinetic energy. The maximum kinetic energy of photo-electron doubles when light of wavelength $500 \mathrm{~nm}$ is used. The workfunction of the metal is : (Take hc $=1230 \,\mathrm{eV}-\mathrm{nm}$ ).
Solution
<p>$\because$ ${K_m} = {{hc} \over \lambda } - \phi$</p>
<p>$\Rightarrow K = {{1230} \over {800}} - \phi$</p>
<p>and, $2K = {{1230} \over {500}} - \phi$</p>
<p>$\Rightarrow 2 \times {{1230} \over {800}} - 2\phi = {{1230} \over {500}} - \phi$</p>
<p>$\Rightarrow \phi = 0.615\,eV$</p>
About this question
Subject: Physics · Chapter: Dual Nature of Matter and Radiation · Topic: Photoelectric Effect
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