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UNIT 2: ENERGY and WAVES (Level 3) written assignment
This written assignment covers assessment criteria 5 and 6
The Photoelectric effect, and the Production of Light
In 1887 Hertz discovered the photoelectric effect, where electrons were emitted from a zinc surface when illuminated with ultra-violet light. These electrons (called ‘photoelectrons’) were only emitted when the frequency of the ultra-violet light was above a certain value (called the ‘threshold frequency’). Criteria 5c
Assume that ultra-violet light is falling onto a piece of zinc, and photoelectrons are being emitted from the surface. As the intensity (brightness) of the ultra-violet light is increased, what happened to the kinetic energy of the photoelectrons? Criteria 5c
Explain why this discovery was not in agreement with the wave model of light. Criteria 5a
Describe the new photon model of light, which was proposed as a result of the photoelectric effect. Criteria 5b
Calculate the energy of a photon of green light, whose frequency is 6 x 1014 Hertz. Criteria 5d
In 1905 Einstein developed an equation that described the photoelectric effect. This equation is hf = + k.e. Explain what the following quantities represent? (i) hf
An atom consists of a nucleus surrounded by electrons. A photon of light is emitted each time one of these electrons loses energy. The type and colour of light emitted depends on the amount of energy lost by the electron. Criteria 6a
Explain the energy level model of the atom.
Under what conditions will a photon of light be emitted? [Hint: use the words ‘electrons’ and ‘excited’ in your answer]. Criteria 6a
The light emitted from a sodium discharge tube (like those found in street lights) can be passed through a prism, so that we can see all the colours emitted by the sodium atoms. Why is light of more than one colour emitted from a single sodium atom? Use a diagram to help illustrate...
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