Question

A voltage of 1.1 V is needed to stop the photocurrent generated when a monochromatic light of wavelength $\lambda =4000A$ is incident on it. Find the work function of metal.

• A. 2.3 eV
  
• B. 2 eV
  
• C. 4.2 eV
  
• D. None pf these
  

Answer 1

The correct option is B 2 eV

Wave length of incident light $\left(\lambda \right)={4000}^{\prime }{A}^{\prime }=400nm$.

So, energy of incident light in given as :

$E=\frac{1240}{\lambda \left(innm\right)}eV=\frac{1240}{400}=3.\perp eV$.

Now stopping potential $=1.\perp V=V_o$

So, KE of emitted photoelectrons was $=e{V}_o=\perp \times 1.1$

$\Rightarrow K=\perp .\perp eV$

Now from einstein photoelectric equations :-

$E=W_o+K$ [$W_o$ = work function]

$\Rightarrow W_o=E-K$

$=3.1-1.1=2eV$