Work function
The minimum energy required to remove an electron from the surface of a material. Represented by Φ (in joules or eV), the work function is a material property that varies with the metal or substance. In the photoelectric effect, hf = Φ + KE_max, where KE_max is the maximum kinetic energy of emitted photoelectrons.
Formula
hf = Φ + KE_max
Real World
Caesium's low work function (2.1 eV) makes it ideal for the photocathodes inside night-vision goggles used by the British Army, where even dim visible light can liberate electrons to form an amplified image.
Exam Focus
Sketch the photoelectric graph (KE_max vs frequency) and label the threshold frequency and work function intercept to secure full marks.
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