Photoelectric Effect

Electricity and Magnetism Level 1

The photoelectric effect is the observation that many metals emit electrons when light shines upon them. Electrons emitted in this manner can be called photoelectrons.

The work function of an element is the minimum energy needed to remove an electron from the solid element. The work function for rubidium is $\SI[per-mode=symbol]{208.4}{\kilo\joule\per\mole}$ .

What is the minimum amount of energy needed to eject a single electron from the surface of rubidium metal?

Details and Assumptions:

$N_A = 6.022 \times 10^{23} \si{\mole}.$
$h = 6.63 \times 10^{-34}\si{\joule\second}.$
$c = 3 \times 10^8\si[per-mode=symbol]{\meter\per\second}.$

5.2\times10^{-22}\text{ J}

6.32 \times 10^{-22}\text{ J}

3.46 \times 10^{-22}\text{ kJ}

2.88 \times 10^{-19}\text{ kJ}

1 solution

Christopher Williams
May 4, 2016

This is mostly a matter of reducing down the given constants. We want to find the energy required for 1 atom.

We're told that the work function for Rubidium is $\SI{208.4}{\kilo\joule\per\mole}$ , so lets find the energy per atom.

$\SI{208.4}{\kilo\joule\per\mole} = \SI{208400}{\joule\per\mole}$
We're given (and know Avogadro's number) that $6.022\times 10^{23}\si{\textrm{atom}\per\mole}$

So $\frac{\SI{208400}{\joule\per\mole}}{6.022 \times 10^{23}\si{\textrm{atom}\per\mole}} = 3.46 \times 10^{-19}\si{\joule\textrm{atom}^{-1}}$ .

You're Right！ =)

Nicole Ling - 5 years, 1 month ago

Photoelectric Effect

1 solution

0 pending reports