Earnshaw Medal
Earnshaw 2008 Nominees: Graeme Cunningham
The Photoelectric Effect
In this experiment the photoelectric effect was investigated with zinc and niobium. Values for the work functions of both metal samples were found to be 4.175V and 4.301V respectively. The contact potential between each sample and the copper chamber was calculated as 0.126V. A value for the work function of the unpolished copper chamber was settled on at 4.605V. The maximum velocity of the electrons emitted from the zinc sample was found to be 4.705x10^5ms^-1.
The electron energy distribution was then modelled for zinc in MATLAB from the IV curves recorded. A deviation from the expected Maxwellian distribution was recorded. The distribution could be roughly fitted with a parabolic function.
The experimental set up was again modified to view the effects of a magnetic field applied perpendicular to the zinc sample with a solenoid. The photoelectron angular distribution was investigated by examining the relationship between the grid and the cathode currents as a function of the magnetic field strength. The earth’s magnetic field had to be cancelled out due to the low magnetic fields used (1-3G).
The experimental set up was rotated by 900 and the same measurements were repeated to view the effect of the earth’s magnetic field explicitly both with and without cancelling out the vertical component.
Supervisor: Dr. Emma Sokell, Dr. John Quinn and Dr. Luis Leon Vintro
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