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18 Mar 2010 14:25:01 IST

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How to calculate stopping potential if wavelength is known?

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How to calculate stopping potential if wavelength is known?

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keshav

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Joined: 30 Nov 2008

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18 Mar 2010 15:22:14 IST

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use Einstein's photoelectric equation :KE(max) = hc/lambda - phi (work function) ( all this in joules) divide this KE max by e ( charge on electron ) to get the potential and rate me !

edison

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18 Mar 2010 18:02:09 IST

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The stopping potential is related to the (maximum) kinetic energy of the ejected electrons by

eV₀ = KE_max = $\displaystyle{\textstyle\frac{1}{2}}$ mv_max².

KE_max = eV₀ = hf - $\displaystyle\phi$ = $\displaystyle{\frac{hc}{\lambda}}$ - $\displaystyle\phi$ .

Thus, a graph such as in Fig. of the stopping potential V₀ vs. the frequency f is a straight line, with slope related to Planck's constant h and x -intercept being the cutoff frequency, f_c where V₀ = 0 :

f_c = $\displaystyle{\frac{\phi}{h}}$ = $\displaystyle{\frac{c}{\lambda_c}}$ ,

where $\lambda_{c}^{}$ is the corresponding cutoff wavelength. This behaviour is observed experimentally, and the success of this explanation made more and more people take the photon picture of light seriously.

**Figure :** Data from a photoelectric effect experiment
$\begin{figure} \begin{center} \leavevmode \epsfxsize=2.0 in \epsfbox{/export/home/fyde/randy/figs/fig27-3.eps}\end{center}\end{figure}$

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