Iron has a work function (φ) of 4.50 ev. what is the longest wavelength of light that will cause the ejection of electrons? (1 ev=1.6 × 10⁻¹⁹ j)

2.75×10^-7m

Explanation:

The work function refers to the smallest energy a photon must posses in order to cause the ejection of electrons from a metal surface.

If Eo= hfo

Eo=work function of the metal

fo=threshold frequency

h= Plank's constant

But Eo= hf= hc/wavelength

Wavelength= hc/Eo

We convert Eo to joules

4.50×1.6×10^-19=7.2×10^-19J

c=3×10^8ms-1

h=6.6×10^-34Js

Wavelength= 3×10^8×6.6×10^-34/7.2×10^-19

2.75×10^-7m

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it means there are 3 atoms of oxygen