Discussion Forum



1)

A metal surface is illuminated by light of two different wavelengths 248nm and 310 nm. The maximum speed of the photoelectrons corresponding to these wavelengths are u1  and u2, respectively. If the ratio u1:u2=2:1 and hc=1240 eV n m, the work  function of the meal  is nearby


A) 3.7 eV

B) 3.2 e V

C) 2.8 e V

D) 2.5 e V

Answer:

Option A

Explanation:

Energy corresponding to 248 nm wavelength

               $= \frac{1240}{248}eV=5eV$

 Energy corresponding to 310 nm wavelength

$= \frac{1240}{310}eV=4eV$

                $= \frac{KE_{1}}{KE_{2}}=\frac{\mu_1^2}{\mu_2^2}=\frac{4}{1}$

                               =  $\frac{5eV-W}{4eV-W}$

  $\Rightarrow$          $  16-4W=5-W$

$\Rightarrow$        11=3W

 $\Rightarrow$       $W=\frac{11}{3}=3.67 eV \cong 3.7eV$