Energy and Waves
1. 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’).
A. 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?
If the intensity of the ultra-violet light is increased, more electrons will be emitted. There will be ...view middle of the document...
The maximum kinetic energy, KE, that any photoelectron can possess is given by hf= φ +KE, where φ is the work function, i.e., the energy required to free an electron from the material, varying with the particular material.
D. Calculate the energy of a photon of green light, whose frequency is 6 x 1014 Hertz.
E=hf f=6 x 1014 h= 6.6 x 10-34
E = (6.6x10-34) x (6 x 1014) = 3.9 x 10-19 Joule
E. In 1905 Einstein developed an equation that described the photoelectric effect. This equation is hf = φ + k.e. Explain what the following quantities represent?
(i) hf = energy of incident photon
h = planck’s constant
f = frequency of the photon.
(ii) Φ = work function
The work function is the minimum amount of energy required to remove an electron from the metal surface.
(iii) K.E = Kinetic energy of freed electron
2. 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.
a. Explain the energy level model of the atom.
Quantum theory explains why atomic emission spectra consist of series sharp lines. Each line in an emission spectrum correspondent to an energy jump of a definite size as electrons drop back from a higher energy level to a lower energy level. The bigger the energy jump, the higher the frequency of electromagnetic radiation...