Edexcel A-Level Physics AS 2.3.60 Threshold Frequency and Work Function Questions

Practise Edexcel A-Level Physics threshold frequency and work function using photoelectric equations, eV conversions and electron kinetic energy.

Exam points

define work function as the minimum energy needed to release a photoelectron from metal
use hf = φ + ½mv²max to calculate work function, metal identity or electron speed
evaluate wavelength and intensity changes by separating photon energy from photon number

[Maximum number: 3]

The diagram shows the energy levels for an atom of hydrogen.

Figure for Question Edexcel A-Level Physics AS 2.3.60 Threshold Frequency and Work Function Questions question 1 — Edexcel A-Level Physics AS

Photons with energy $1.63\times10^{-18}\,\mathrm{J}$ are incident on a metal plate. The surface releases electrons due to the photoelectric effect.

Calculate the maximum possible speed of the electrons.

Work function $\Phi=5.89\times10^{-19}\,\mathrm{J}$ .

The maximum kinetic energy is $E_k=hf-\Phi=1.63\times10^{-18}-5.89\times10^{-19}=1.04\times10^{-18}\,\mathrm{J}.$ Using $E_k=\tfrac12m_ev_{\max}^2$ , $v_{\max}=\sqrt{\frac{2E_k}{m_e}}=1.5\times10^6\,\mathrm{m\,s^{-1}}.$

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Edexcel A-Level Physics AS 2.3.60 Threshold Frequency and Work Function Questions question 1