g the light from illuminating the sodiumplate, the current will then stop. When the amountof light striking the plate is increased, the amountof current also increases. If various colours of lightare tested on the sodium plate it will be discoveredthat violet and blue light causes current flow.However, colours of light toward the other end ofthe spectrum (red) do not result in a flow ofelectric current when they illuminate the sodiumplate. The electrons will only be emitted if thefrequency of the radiation is above a certainminimum value, called the threshold frequency(fo). The threshold frequency varies with eachmetal. When the sodium plate was exposed tohigh frequency light, electrons were emitted andwere attracted to the positive terminal, causing aflow of current. However, when a low frequencylight was used no electrons were emitted andtherefore there was no current. Observations ofthe Photoelectric Effect 1. Current flows as soonas the negative terminal is illuminated. 2. Highfrequency light causes electrons to be emitted fromthe sodium, however, a lower frequency light doesnot. 3. The energy of the emitted electrons doesnot depend upon the intensity (brightness) of thelight, it is dependent on the frequency of the light.A higher frequency of light causes higher energyelectrons. 4. The amount of current that flows isdependent upon the intensity (brightness) of thelight. Prior to the 1900’s light was considered tobe wave-like in nature. This was due to thesuccess of Maxwell’s Electromagnetic Theory.However, much of the phenomenon observedduring the photoelectric effect was in contradictionto the Wave Theory of Light. For instance, theenergy contained in electromagnetic waves, andthe amount of energy that would strike a sodiumelectron can be calculated. Such a calculationshows that an electron could indeed gain enoughenergy to be liberated from the sodium, but onlyafter the sodium had been illuminated for severalhours. Ho...
