Page 251 - Physics Form 5 KSSM_Neat

Problem Solving Using Einstein's Photoelectric Equation CHAPTER 7

LET’S ANSWER
Example 1 LET’S ANSWER Quantum Physics

A blue light with a frequency of 6.67 × 10 Hz is shone on a clean
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caesium metal surface. What is the maximum kinetic energy of
KEMENTERIAN PENDIDIKAN MALAYSIA
photoelectrons emitted?
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[Work function of caesium = 3.43 × 10 J, Planck’s constant = 6.63 × 10 J s] https://bit.
ly/2YwWUsj
Solution

Step 1: Step 2: Step 3: Step 4:
Identify the Identify the Identify the Solve the problem
problem information given formula to be used numerically

1 Maximum kinetic energy of the 3 hf = W + K
max
photoelectron, K
max
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4 (6.63 × 10 )(6.67 × 10 ) = 3.43 × 10 + K
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2 Frequency, f = 6.67 × 10 Hz max
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Work function, W = 3.43 × 10 J K max = 4.42 ×10 − 3.43 × 10
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Planck's constant, h = 6.63 × 10 J s = 9.92 × 10 J
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Example 2

Figure 7.14 shows the change in kinetic energy of K / eV
photoelectrons released from lithium for different light
frequencies. Determine the threshold frequency from 2.0
the graph and calculate the work function of lithium. 1.8
[Planck's constant, h = 6.63 × 10 J s] 1.6
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1.4
Solution 1.2
1.0
Threshold frequency, f = 5.6 × 10 Hz 0.8
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0
Planck’s constant, h = 6.63 × 10 J s 0.6
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Work function, W = hf 0 0.4
= (6.63 × 10 ) (5.6 × 10 ) 0.2
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= 3.71 × 10 J 0
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1 2 3 4 5 6 7 8 9 10
f / 10 Hz
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Figure 7.14

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