Page 249 - Physics Form 5 KSSM_Neat

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Work Function and Threshold Frequency for Photoelectric Effect CHAPTER 7
The minimum energy required for a photoelectron to be emitted from a metal surface is
known as work function. The minimum frequency for a light photon to produce photoelectric
effect is called threshold frequency. Quantum Physics

1 The relationship between the maximum kinetic energy of photoelectrons, K max and the light
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frequency, f is shown by the graph in Figure 7.12. The graph is a straight line with a positive
KEMENTERIAN PENDIDIKAN MALAYSIA
gradient and not passing through the origin. The threshold frequency, f is the value of the
0
intercept on the frequency axis.
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No photoelectric
effect Photoelectric effect exists
K max

f
0 f 0

Figure 7.12 Graph of K against f
max
The relationship between work function and threshold frequency of a metal can be
determined by the relationship W = hf . Photoelectrons will acquire kinetic energy when light
0
frequency exceeds threshold frequency. The higher the threshold frequency of a metal, the higher
the work function. This means the minimum energy required for photoelectric effect to occur is
higher. Different metals have different threshold frequencies as shown in Figure 7.13.

K max
Metal A B C

Graphs with the
same gradient
f
0 f f f
0, A 0, B 0, C

Figure 7.13 Graphs of K against f for different types of metals
max

LS 7.3.1 7.3.2 7.3.3 239