Physics (AS & A Level) · Oct / Nov 2016 · Paper 43 · Question 10

electromagnetic radiation/photons incident on a surface causes emission of electrons (from the surface) [2]

E = hc / λ = (6.63 × 10–34 × 3.00 × 108) / (436 × 10–9) = 4.56 × 10–19 J (4.6 × 10–19 J) [2]

Φ = hc / λ0 λ0 = (6.63 × 10–34 × 3.00 × 108) / (1.4 × 1.60 × 10–19) = 890 nm [2]

λ0 = (6.63 × 10–34 × 3.00 × 108) / (4.5 × 1.60 × 10–19) = 280 nm [1]

caesium: wavelength of photon less than threshold wavelength (or v.v.) or λ0 = 890 nm > 436 nm so yes tungsten: wavelength of photon greater than threshold wavelength (or v.v.) or λ0 = 280 nm < 436 nm so no [2]

11 in metal, conduction band overlaps valence band/no forbidden band/no band gap as temperature rises, no increase in number of free electrons/charge carriers as temperature rises, lattice vibrations increase (lattice) vibrations restrict movement of electrons/charge carriers (current decreases) so resistance increases [5]