Presentation on theme: "The Photoelectric Effect A level At The Sixth Form College Colchester."— Presentation transcript:
The Photoelectric Effect A level At The Sixth Form College Colchester
Quantum Physics 1901 Max Planck initiated Quantum Physics with his explanation of Black Body Radiation (Nobel Prize 1918) Black Body radiation had proved impossible to explain using classical theories of physics
A Black Body Defined as a body that absorbs ALL the radiation that falls on it All black bodies in the room do reflect – we can see them – they are not Black Bodies The nearest we can get to a true Black Body is a hole –All radiation that falls on a hole goes through –None is reflected
Black Body Spectrum Although the Black Body does not reflect energy – it does emit energy The spectrum of Black Body radiation is a very special shape, visible infra redultra violet
Plancks Explanation Radiation is emitted (but did not stay) in small packets, he called them quanta (or photons) The energy E of a packet is given by the equation –E = hf Where f is the frequency h is Plancks constant h = x Js
Einstein 1905 Einstein extended Plancks work by saying that light remains in its photon packets He used this to explain the photoelectric effect (Nobel Prize 1921 – not won for Relativity)
The Photoelectric Effect In the photoelectric effect, electrons are emitted from a metal surface when it is exposed to light The conditions for this are very particular, and there were problems explaining them with classical physics
Gold Leaf Electroscope gold leaf clean zinc Attached to the top is a zinc plate – which has been cleaned of its oxide layer. The gold leaf is attached at the bottom, inside the case.
Gold Leaf is Repelled Excess electrons repel each other. They gather at top and bottom. The gold leaf is repelled from the metal shaft.
Photo Electrons incoming photon ejected electron Incoming photons fall onto the clean zinc surface. Electrons are ejected from the surface.
Discharged Electroscope As the electrons leave the surface, the gold leaf is less repelled from the metal shaft. It falls slowly down.