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A beam of light of wavelength λ is incident on a clean metal surface and photoelectrons are emitted - AQA - A-Level Physics - Question 10 - 2017 - Paper 1
Question 10
A beam of light of wavelength λ is incident on a clean metal surface and photoelectrons are emitted. The wavelength of the light is halved but energy incident per se... show full transcript
Worked Solution & Example Answer:A beam of light of wavelength λ is incident on a clean metal surface and photoelectrons are emitted - AQA - A-Level Physics - Question 10 - 2017 - Paper 1
Step 1
Maximum kinetic energy of the emitted photoelectrons
Answer
The maximum kinetic energy of the emitted photoelectrons depends on the frequency of the light. When the wavelength is halved, the frequency of the light doubles (since frequency and wavelength are inversely related:
y = rac{c}{f},
where y is the wavelength, c is the speed of light, and f is the frequency). According to the photoelectric effect, the kinetic energy (K.E.) can be expressed as:
where h is Planck's constant. Therefore, with increased frequency, the maximum kinetic energy of the emitted photoelectrons increases. Hence, the answer is "Increases".
Step 2
Number of photoelectrons emitted per second
Answer
Since the energy incident per second remains the same, the number of photons incident per second depends on the energy of each photon. When the wavelength is halved, the energy of each photon increases, which means fewer photons are needed to maintain the same total energy incident per second. As a result, the number of emitted photoelectrons per second decreases. Therefore, the answer is "Decreases".