Question

When a metal surface is illuminated by light of wavelengths $400nm$ and $250nm$, the maximum velocities of the photoelectrons ejected are $V$ and $2V$ respectively. The work function of the metal is

• A. $2hc\times {10}^{6}J$
• B. $1.5hc\times {10}^{6}J$
• C. $hc\times {10}^{6}J$
• D. $0.5hc\times {10}^{6}J$

Answer 1

Answer: (A)

$2hc\times {10}^{6}J$

$hc/400=WF+KE$---eq 1
$hc/250=WF+4KE$---eq 2
(eq 1)$\times$4-eq 2
$hc/100-hc/250=3WF$ Note:- substitute in proper units. The wavelengths are in nm. Convert them into meters.