Discussion Forum

1)

If the maximum kinetic energy of emitted electrons in photoelectric effect is 3.2 x 10^-19 J and the work-function for metal is

6.63 x10^-19 J, then stopping potential and threshold wavelength respectively are

[Planck's constant,h=6.63 x10³⁴ J-s]

[ Velocity of light , c=3 x10⁸ m/s]

[charge on electron =1.6 x10^-19 C]

Answer:

Option C

Explanation:

 The maximum kinetic energy of emitted photo electron is 

K_max = eV_s

where V_s= stopping potential.

$\Rightarrow   V_{s}=\frac{K_{max}}{e}=\frac{3.2\times 10^{-19}}{1.6\times 10^{-19}}=2V$

 Also, the work function of a metal is

$\phi=\frac{1242}{\lambda_{0}(nm)}eV$

 $\lambda_{0}=\frac{1242\times1.6\times 10^{-19}}{\phi}nm$

$\Rightarrow$    $\frac{1242\times 1.6\times 10^{-19}}{6.63 \times 10^{-19}}nm$

 = 3000  Å