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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 ?.
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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 (fo), 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 Planck’s Constant. • There is a certain minimum energy needed to release an electron – called the Work Function given by W=hfo.
Equations • To release an electron, hf > hfo. • If hf < hfo, no electrons will be released. • The kinetic energy of the released electrons is given by Ek = hf – hfo.