Question

Tungsten has work function $4.8eV$, we wish to use tungsten as photo-cathode with a $600nm$ wavelength .What shall we do?

• A. Coat tungsten with cesium
• B. Oxide coat tungsten
• C. $C{u}_2{O}_2$be coated on tungsten
• D. cool the tungsten

Answer 1

The correct option is B Oxide coat tungsten

The energy of radiation must be equal to or greater than the work functions of metals to show photoelectric effect.
Here the energy of the radiation is $E=hc/\lambda$

$E=\frac{6.626\times {10}^{-34}Js\times 3.0\times {10}^{-8}m/s}{600\times {10}^{9}m}$

$=3.3\times {10}^{-19}J$, Now

We know that:

$1J=6.24\times {10}^{18}eV.$

Therefore ,

$3.3\times {10}^{-19}J=3.3\times {10}^{-19}\times 6.24\times {10}^{18}eV=2.18eV.$

Now Tungsten has work function 4.8eV. So we need to do Oxide coating to get photoelectric effect.