A Level Physics Practice Exam

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How can the threshold frequency of cathode material be calculated using wavelength?

f = λ/c
f = c * λ
f = c/λ
f = 1/(c/λ)

The correct answer is: f = c/λ

In the context of the photoelectric effect, the threshold frequency of a material is the minimum frequency of light required to eject electrons from the surface of the cathode. This frequency is inversely related to the wavelength of the light being used. The relationship between frequency (f), wavelength (λ), and the speed of light (c) is given by the equation: \[ c = f \cdot λ \] From this equation, we can rearrange it to isolate frequency, which leads to the formula: \[ f = \frac{c}{λ} \] This means that the frequency is calculated by dividing the speed of light by the wavelength. Therefore, if you know the wavelength of the light incident on the cathode material, you can easily find the frequency by applying this relationship. In summary, the correct expression for calculating threshold frequency using wavelength is that frequency is equal to the speed of light divided by the wavelength, which corresponds perfectly with the choice made.