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The work function of a substance is $4.0 \mathrm{eV}$. Then longest wavelength of light that can cause photoelectron emission from this substance approximately
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$310 \mathrm{~nm}$
$310 \mathrm{~nm}$
$\frac{\mathrm{hc}}{\lambda}=\mathrm{W}$
$\lambda_{\text {longest }}=\frac{\mathrm{hc}}{\mathrm{W}}=\frac{6.6 \times 10^{-34} \times 3 \times 10^8}{4.0 \times 1.6 \times 10^{-19}}$
$\Rightarrow \lambda_{\text {longest }} \approx 310 \mathrm{~nm}$.
$\lambda_{\text {longest }}=\frac{\mathrm{hc}}{\mathrm{W}}=\frac{6.6 \times 10^{-34} \times 3 \times 10^8}{4.0 \times 1.6 \times 10^{-19}}$
$\Rightarrow \lambda_{\text {longest }} \approx 310 \mathrm{~nm}$.
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