Question

The work function of a metal is 4.2 eV. If the radiation with wavelength 2000 $\stackrel{0}{A}$ falls on the metal surface then the kinetic energy of fastest photo electron will be:

• A.
  $1.6\times {10}^{-19}$ J
• B.
  $1.6\times {10}^{-10}$ J
• C.
  ​​​​​​​$3.2\times {10}^{-19}$ J
• D.
  ​​​​​​​$6.4\times {10}^{-10}$ J

Answer 1

The correct option is C

​​​​​​​$3.2\times {10}^{-19}$ J
Given,
Wavelength of the incident radiation $=2000$ $\stackrel{\circ }{A}$
Work function = 4.2 eV
Again,
We know,
$E\left(eV\right)=\frac{12400}{\lambda \stackrel{\circ }{A}}=\frac{12400}{2000}=6.2eV$


According to Einstein photoelectric effect,
Kinetic energy
$=h\nu -\text{work function}$
$=6.2-4.2eV$
$=2eV=3.2\times {10}^{-19}J$