The Photoelectric Effect Key Points

What is it ? Electrons are emitted from zinc when ultraviolet radiation shines on it. Other metals emit electrons with other kinds of radiation.

Why was it a problem ? If the frequency of the radiation was reduced below the Threshold Frequency (f o ), no electrons were emitted. No-one could explain this using wave theory.

What did Einstein say ? We must think of light as a particle and not as a wave. Each particle carries energy given by E=hf where h is Plancks Constant. There is a certain minimum energy needed to release an electron – called the Work Function given by W=hf o.

Equations To release an electron, hf > hf o. If hf < hf o, no electrons will be released. The kinetic energy of the released electrons is given by E k = hf – hf o.