Modern Physics 2 Question 19
18. The work function of a substance is $4.0 eV$. The longest wavelength of light that can cause photoelectron emission from this substance is approximately
$(1998,2 M)$
(a) $540 nm$
(b) $400 nm$
(c) $310 nm$
(d) $220 nm$
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Solution:
- $\lambda($ in $\AA)=\frac{12375}{W(eV)}=\frac{12375}{4.0} \AA \approx 3093 \AA$
or $\lambda \approx 309.3 nm \approx 310 nm$
NOTE $\lambda($ in $\AA)=\frac{12375}{W(e V)}$ comes from $W=\frac{h c}{\lambda}$
