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Published byKatherine Simmons Modified over 6 years ago
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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)
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The photoelectric effect
- - - - - - - - - - - Electrons from well below the surface are more difficult to remove
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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 -
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The picoammeter registers a tiny current when light of the correct frequency falls on the metallic electrode.
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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)
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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
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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 × J.
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