Question

If the work function of a potential is $6.875$eV, its threshold wavelength will be (Take $=c=3\times {10}^{3}m/s$).

• A. $3600\stackrel{o}{A}$
• B. $2400\stackrel{o}{A}$
• C. $1800\stackrel{o}{A}$
• D. $1200\stackrel{o}{A}$

Answer 1

Answer: (C)

$1800\stackrel{o}{A}$

$W=\frac{hc}{\lambda }$
where h is planck's constant, c is speed of light, $\lambda$ is wavelength
$\lambda =\frac{hc}{W}=\frac{6.6\times {10}^{-34}\times 3\times {10}^8}{6.825\times 1.6\times {10}^{-19}}$
$\lambda =1800\stackrel{o}{A}$.