The cut off frequency of the magnesium atom is obtained as 8.9 * x 10^18 Hz.
The cut off frequency is the lowest frequency of the incident ray at which photoelectric effect occurs.
Given that;
1 eV gives 1.60 x 10-19 J
3.70 eV gives 3.70 eV * 1.60 x 10-19 J/1 eV
= 5.92x 10^-19 J
Now;
Wo = hfo
fo = Wo/h
fo = 5.92x 10^-19 J/6.6 * 10^-34
fo = 8.9 * x 10^18 Hz
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