Question

Platinum, which is widely used as a catalyst, has a work function φ(the minimum energy needed to eject an electron from the metal surface) of 9.05 x 10-19 . What is the longest wavelength of light which will cause electrons to be emitted?
A. 2.196×10-7m
B. 4.553×10-6 m
C. 5.654 x 102 m
D. 1.370 x 1015 m
E. >106 nm

Answer 1

Answer:

A. $\lambda_0=2.196\times 10^{-7}\ m$

Explanation:

The work function of the Platinum = $9.05\times 10^{-19}\ J$

For maximum wavelength, the light must have energy equal to the work function. So,

$\psi _0=\frac {h\times c}{\lambda_0}$

Where,  

h is Plank's constant having value $6.626\times 10^{-34}\ Js$

c is the speed of light having value $3\times 10^8\ m/s$

$\lambda_0$ is the wavelength of the light being bombarded

$\psi _0=Work\ function$

Thus,

$9.05\times 10^{-19}=\frac {6.626\times 10^{-34}\times 3\times 10^8}{\lambda_0}$

$\frac{9.05}{10^{19}}=\frac{19.878}{10^{26}\lambda_0}$

$9.05\times \:10^{26}\lambda_0=1.9878\times 10^{20}$

$\lambda_0=2.196\times 10^{-7}\ m$