CAIE A-Level Physics 22.2.4 The Photoelectric Equation

Practise applying hf = Φ + ½mv_max² to calculate photoelectron energy, stopping potential or frequency and interpret the associated graphs.

Exam points

calculate maximum photoelectron kinetic energy using hf = Phi + 1/2mv_max²
rearrange the photoelectric equation to determine frequency, work function or maximum speed
convert photon and electron energies consistently and interpret threshold conditions

[Maximum number: 2]

In an experiment, electromagnetic radiation of frequency f is incident on a metal surface.

The results in Fig. 10.1 show the variation with frequency f of the maximum kinetic energy $E_{\text {MAX }}$ of electrons emitted from the surface.

Fig. 10.1

Determine the work function energy in J of the metal used in the experiment.
work function energy = J

Correct read off from graph of f as $5.45 \times 10^{14} \mathrm{~Hz}$ when $E_{\text {MAX }}=0$ $5.45 \times 10^{14} \times 6.63 \times 10^{-34}$

C1

$=3.6 \times 10^{-19} \mathrm{~J}$

A1

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22.2.4—Hf = Φ + 1/2 mvmax 2 question 1