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#

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?

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Answer 2

Benjamin Asiedu

The work function of the metal is approximately 4.02 eV.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.