Photoelectron energy determines its maximum speed
The photoelectric equation gives maximum electron kinetic energy. The classical kinetic-energy equation then converts it into a maximum speed.
Follow the reasoning
- Calculate the energy left after overcoming the work function.
- Convert electronvolts to joules if needed.
- Use the electron mass to calculate maximum speed.
Try it in a past paper 2
Open the question, then use its mark scheme to check your work.
Question 6
Use photon energy and work function to find photoelectron kinetic energy.
Build the supporting skills. Practise the photoelectric energy balance first. This question does not ask you to convert the electron kinetic energy into a speed.
Question 8
Use threshold frequency and photoelectron energy to find the incident wavelength.
Build the supporting skills. Practise the photoelectric energy balance first. This question does not ask you to convert the electron kinetic energy into a speed.
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Put the ideas to work
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Specification outcomes (3)
- 4.5.2(c) Use Einstein’s photoelectric equation hf = Φ + KEmax.
- 4.5.2(d) Define work function and threshold frequency.
- 3.3.2(a) Define and calculate kinetic energy, Ek = ½mv², and derive it from first principles.