Guide:
Here is a comprehensive guide on how to calculate the threshold frequency of quantum energy:
- To calculate threshold frequency, we need to read and understand the question.
2. Read the question for the first time.
3. Try reading the question again, but this time underline any numerical figures.
4. Think of the formula that best fits the question
5. The formula for the frequency (f) of quantum energy is f = c/ λ [where c=speed of light in vacuum, and λ=wavelength of the radiation]
6. Relate the variables from the formula with what you have underlined
7. Update your data
8. Solve the problem
10. Another formula we can apply to calculate threshold frequency involves the question that mentioned the work function of a metal which is f0 = w0/h [ where f0 = threshold frequency, w0 = work function of a metal, and h= Planck’s constant = 6.6×10-34Js
Examples of How to Calculate the Threshold Frequency of Quantum Energy
Here are a few examples to guide you.
Example 1
Calculate the frequency of quantum of quantum energy carried by radiation of wavelength 3 x 10-6m, where c is the speed of electromagnetic waves which is about 3 x 108m/s.
Solution
Data:
Wavelength of the radiation, λ = 3 x 10-6m
Speed of light in vacuum, c = 3 x 108m/s
Frequency, f = ?
since f = c/ λ
We can substitute our data into the above formula for frequency
f = 3 x 108/3 x 10-6 = 1014Hz
Therefore, the frequency of quantum of energy is 1014Hz
Example 2
The work function of metal sodium is 20ev. If Planck’s constant is 6.6×10-34Js, calculate the threshold frequency of the metal.
Solution
Data:
The work function, w0 = 20ev = 3.2×10-19J
speed of light in vacuum, c = 3×108m/s
Planck’s constant, h=6.6×10-34Js
f0 = ?
We substitute our formula f0 = w0/h to get
f0 = 3.2×10-19/6.6×10-34 = 4.8×1014
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Reference
