Question

The work function of substances is 4eV. What is the longest wave length of light that can cause the emission of photo electric from this substances?

Answer 1

Answer on Question#50774 – Physics – Nuclear Physics

Question

The work function of substance is $4\,eV$. What is the longest wavelength of light that can cause the emission of photoelectrons from this substance?

Solution

$$A = \frac{hc}{\lambda} + K$$

, where $A$ – work function, $K$ – kinetic energy of photoelectron, $h$ – Planck constant, $c$ – speed of light, $\lambda$ – wavelength.

If we are looking for the longest wavelength, we set $K = 0$, than:

$$A = \frac{hc}{\lambda}$$ $$\lambda = \frac{hc}{A}$$ $$h = 4.136 * 10^{-15}\,eV\,s$$ $$c = 3 * 10^{8} \frac{m}{s}$$ $$\lambda = 4.136 * 10^{-15} * 3 * 10^{8} * \frac{1}{4} = 3.102 * 10^{-7}\,m = 310.2\,nm$$

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