Photoelectric equation is just an energy equation. Energy is a scalar like money. If you have money , I am sure you are not bothered about its unit may it be US$ or S$ or M$ . The one principle must hold true is when you add or subtract , you got to make sure that they have the same units.
The two units used in photoelectric equation are J and eV.
The conversion rate is 1eV = 1.6x 10-19J.
Photon energy = work function + kinetic energy
(6eV) = (4eV) + (2eV) lets say
Using eV is like saying applying 6V of energy to the electron and it takes 4V to extract the electron from the surface and the electron has only 2V of kinetic energy left. Almost not requiring any memory work as if you have six thousand dollar and spending 4k on airfare and left with 2 k to spend when you arrive at the airport .
If 2V is applied to the electron (in reverse polarity) the electron will have no kinetic energy left . So we say stopping voltage is 2V.
(9.6 x10-19J) = (6.4 x 10-19J) + (3.2 x 10-19J)
Now convert them all back to Joule the equation looks almost incomprehensible and therefore scientist like to use eV. You wouldn't want to use rupees in singapore.
For examination purposes , as students are not yet scientist , answers in joules are required but some information in eV needs to be converted to joules first before you can use the equation correctly.
