Experimental Investigation of the Photoelectric effect Set up the circuit to supply an opposing Voltage to measure the (maximum) kinetic energy of the electrons Adjust the variable voltage supply until the current is zero. This voltage is called the cut-off voltage. Note how the cell is arranged – where it is ‘pushing’ electrons Measure the cut-off voltage for different light frequencies and plot data on a graph. Convert Voltage to Kinetic energy V= Energy / charge so E = qV Ek = eV where e is the charge on 1 electron 1 electron volt =1 eV = 1.6 x 10-19 J f V f Ek

Ek fo f -ϕ Terms & Definitions: Gradient = h -ϕ Kinetic energy vs. frequency: Terms & Definitions: Threshold frequency (fo) the minimum frequency of light that results in the emission of photoelectrons Work function (ϕ) the minimum amount of work needed to eject an electron from the surface ϕ = h fo Stopping potential (V) equivalent to the maximum kinetic energy of the ejected photoelectrons (Ek)

What is the gradient?