Question

Light with a frequency of `2.79 * 10^15 Hz` strikes a metal surface and ejects electrons that have a maximum kinetic energy of `6.4 eV`. What is the work function of metal?

Answer 1

I found: `phi=8.2577xx10^-18J~~8.26xx10^-19J=5.2eV`

Explanation:

Here you deal with the Photoelectric Effect where Energy (in form of light) strikes a metal surface and ejects electrons from it.
But:
the maximum kinetic energy of, say, one electron emitted will be equal to the incident (photon) energy given as `hf` (Planck's Constant times frequency) minus the energy that "binds" the electron to the metal (the work function `phi`).
So basically:
`K=hf-phi`
Kinetic Energy (max) is `K=6.4eV=6.4*1.6xx10^-19=1.024xx10^-18J`

So we get:
`1.024xx10^-18=6.63xx10^-34*2.79xx10^15-phi`
so:
`phi=8.2577xx10^-18J~~8.26xx10^-19J=5.2eV`

Nickel perhaps?