Cambridge International AS and A level Physics
8 This graph shows the variation with frequency f of the maximum kinetic energy EK of the electrons emitted from the surface of a metal:
Ek / 10−19 J
12 8 4 0
−4
0
1.0
2.0
f / 1014 Hz
a Use the photoelectric equation to show that the gradient of the graph is equal to Planck’s constant. b Obtain a value for Planck’s constant from the graph. c State how the work function energy ϕ can be obtained from the graph. d Obtain a value for the work function energy. Imagine that the graph is redrawn for a metal with a smaller work function. e State how the gradient and intercept of the new graph compare with the old graph.
198
Exercise 30.3 Line spectra and band theory This exercise tests your understanding and interpretation of line spectra, and gives you practice calculating energies including band gaps. 1 This diagram shows energy levels of the hydrogen atom: Energy / 10−18 J 0 −0.06 −0.09 −0.14 −0.24 −0.54
−2.18
An electron is on the energy level at −0.24 × 10 −18 J. The electron can emit or absorb a photon to change levels.