Discussion Forum

1)

A silver sphere of radius 1 cm and work function 4.7 eV is suspended from an insulating thread in free-space. It is under continuous illumination of 200 nm wavelentth light. As phottelectrons are emitted, the sphere gets charged and acquires a potential. The maximum number of photoelectrons emitted from the sphere  is $A \times 10^{z}$

(where 1< A < 10). The value of Z is 

Answer:

Option D

Explanation:

Photoemission will stop when the potential on silver sphere becomes equal to the stopping potential.

$\therefore$   $\frac{hc}{\lambda}-W=eV_{0}$

 Here, $V_{0}=\frac{1}{4 \pi \epsilon_{0}} \frac{ne}{r}$

$\therefore$  $\left(\frac{1240}{1200}eV\right)-(4.7 eV)=\frac{9\times10^{9}\times n \times1.6 \times10^{-19}}{10^{-2}}$

$(6.2-4.7)=\frac{9\times10^{9}\times n \times1.6 \times10^{-19}}{10^{-2}}$

or   $n=\frac{1.5\times10^{-2}}{9\times 1.6\times10^{-10}}=1.04\times10^{7}$

 $\therefore$  Answer is 7