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Atomic and Nuclear Physics Investigating the Photo-Electric Effect Relation between Photo-Current and Intensity of Light The intensity of light at a distance, r from a point (small) light source is inversely proportional r2.
If the photo-current, Ip, is measured with the light source at different distances, r, we find Ip is proportional to 1/r2. We therefore conclude that the photo-current is directly proportional to intensity of light*. * or other electro-magnetic radiation; ultra-violet, infra-red etc.Relation between Photo-electric Emission and Colour of Light In the wave model of electro-magnetic radiation, different colours of light correspond to different wavelengths (or frequencies).
In the diagram above, the arrow representing the current, Ip, is drawn in the sense of electron current (not conventional current).The coloured filter allows a narrow range of wavelengths to pass through it. A variable voltage supply is connected in opposition to the photo-electric cell. A coloured filter is put in place. The voltage of the supply is gradually increased until Ip is reduced to zero. This voltage is called the stopping voltage, Vs.Knowing this voltage allows us to calculate the kinetic energy (K.E.max) with which the most energetic electrons were emitted from the photo-emissive surface. It is found that
These observations are summarised in the laws of photo-electric emission.
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© David Hoult 2009 |
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