Explain how each observation provides support for the particle theory but not the wave theory of light.

Determine a value for Planck’s constant.

State what is meant by the work function of a metal.

Calculate the work function of barium in eV.

The experiment is repeated with a metal surface of cadmium, which has a greater work function. Draw a second line on the graph to represent the results of this experiment.

Observation 1:
particle – photon energy is below the work function
OR
E = hf and energy is too small «to emit electrons»
wave – the energy of an em wave is independent of frequency

Observation 2:
particle – a single electron absorbs the energy of a single photon «in an almost instantaneous interaction»
wave – it would take time for the energy to build up to eject the electron

attempt to calculate gradient of graph = «\(\frac{{4.2 \times {{10}^{ - 19}}}}{{6.2 \times {{10}^{14}}}}\)»

\( = 6.8 - 6.9 \times {10^{ - 34}}\) «Js»

Do not allow a bald answer of 6.63 x 10^-34 Js or 6.6 x 10^-34 Js.

ALTERNATIVE 1
minimum energy required to remove an electron «from the metal surface»

ALTERNATIVE 2
energy required to remove the least tightly bound electron «from the metal surface»

ALTERNATIVE 1
reading of y intercept from graph in range 3.8 − 4.2 × 10^–19 «J»
conversion to eV = 2.4 – 2.6 «eV»

ALTERNATIVE 2
reading of x intercept from graph «5.8 − 6.0 × 10¹⁴ Hz» and using hf₀ to get 3.8 − 4.2 × 10^–19 «J»
conversion to eV = 2.4 – 2.6 «eV»

line parallel to existing line
to the right of the existing line