Answer: Replace the orange light source with a higher frequency light source
Explanation:
To expel electrons from a piece of metal, the incoming light must have a minimum frequency to cause a photoelectric effect, i.e., the ejection of photoelectrons from a metal surface, which is also known as the metal's threshold frequency.
If v = frequency of incident photon and vth= threshold frequency, then,
Therefore, we would have to increase the frequency of incident light so that it becomes greater than the threshold frequency of that surface, and consequently a photoelectric process takes place.