The photons which strike the surface have to supply the energy to escape the surface ( the work function (φ) and the kinetic energy of the electrons (KE)

The photoelectric effect - - - - - - - - - - - Electrons from well below the surface are more difficult to remove

The left over energy from the photon is exhibited as kinetic energy of the moving electron 1/2mv2 The photon energy E= hf The electron has to escape the surface ie overcome attractive forces this bit of energy is the WORK FUNCTION Φ hf=1/2mv2max+Φ -

The picoammeter registers a tiny current when light of the correct frequency falls on the metallic electrode.

The maximum kinetic energy of the photoelectrons emitted graphed against the frequency of the incident radiation From hf=KEmax+Φ KEmax=hf- Φ KE max Frequency of light Hz This is the threshold frequency of the light below which no photoelectrons are emitted from the surface F (Hz)

Interpreting the graph KEmax F (Hz) So: Gradient = h This is the equation of a straight line. Comparing y=mx+c We can see that h is the gradient of this graph. The intercept on the y axis is equal to (-φ) -φ

In the apparatus shown, monochromatic ultraviolet radiation is incident on the surface of metal X. Photoelectrons are emitted from X and are collected at electrode Y. Y X A (a) Calculate the work function of X, given that each photon in the incident radiation has 3.2 × 10-19J of energy. The maximum kinetic energy possessed by a single photoelectron is 2.1 × 10-19 J.