During an experiment, two learners obtained the work functions of three different metals as
shown below:
Material Work Function (W0
) in J
Aluminium 6,50 × 10–19
Zinc 6,88 × 10–19
Silver 7,23 × 10–19
7.1 Identify the independent variable in this experiment.
(1)
7.2 Identify the dependent variable in this experiment.
(1)
7.3 Explain what the differences in the work functions of the listed metals in the table mean.
(2)
7.4 Violet light, with a wavelength of 410 nm, is shone onto all three of the metal surfaces.
Show with a calculation which these metals will emit electrons.
(4)
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Physical Science – Assignment 6
7.5 Calculate the speed of an electron that is ejected from the aluminium surface when UV light,
with a wavelength of 170 nm is shone onto the surface.
(5)
7.6 What conclusion can be drawn from the photoelectric effect regarding the nature of light
7.1 The independent variable in this experiment is the different metals (Aluminium, Zinc, Silver).
7.2 The dependent variable in this experiment is the work function of each metal.
7.3 The differences in the work functions of the listed metals indicate how difficult it is to remove electrons from the surface of each metal. A lower work function means that it is easier to release electrons from the surface of the metal when light is shone on it.
7.4 To determine which of the metals will emit electrons when violet light with a wavelength of 410 nm is shone on them, we can calculate the energy of the light using the formula E = hc/λ, where h is Planck's constant, c is the speed of light, and λ is the wavelength. Then we can compare this energy to the work function of each metal to see if it is enough to eject electrons.
7.5 To calculate the speed of an electron ejected from the aluminium surface when UV light with a wavelength of 170 nm is shone on it, we can use the equation Ekmax = hf - W0, where Ekmax is the maximum kinetic energy of the ejected electron, h is Planck's constant, f is the frequency of the light (calculated using f = c/λ), and W0 is the work function of aluminium. Then we can calculate the speed of the electron using the formula v = √(2Ekmax/m), where m is the mass of an electron.
7.6 The conclusion that can be drawn from the photoelectric effect regarding the nature of light is that light behaves as discrete packets of energy called photons, rather than a continuous wave. This is evident from the fact that electrons are only ejected from a metal surface when the light shining on it has a sufficiently high energy, which is determined by the frequency or wavelength of the light.