(i)     Distinguish between an insulator and a conductor.

(ii)     Outline what is meant by the internal resistance of a cell.

State what is meant by the photoelectric effect.

(i)     Suggest why the work function for caesium is smaller than that of mercury.

(ii)     Ultraviolet radiation of wavelength 210 nm is incident on the surface of mercury. The work function for mercury is 4.5 eV. Determine the maximum kinetic energy of the photoelectrons emitted.

An exact determination of the location of the electron in a hydrogen atom is not possible. Outline how this statement is consistent with the Schrödinger model of the hydrogen atom.

(i)     conductor has free electrons/charges that are free to move within/through it / insulator does not have free electrons/charges that are free to move within/ through it;

electrons act as charge carriers;

when a pd acts across a conductor a current exists when charge (carriers) move;

Do not allow “good/bad conductor/resistor” or reference to conductivity/ resistivity.

(ii)     some of the power/energy delivered by a cell is used/dissipated in driving current through the cell;

power loss can be equated to \({I^2}r\) where r represents the (internal) resistance of the cell; } (symbols must be defined)

resistance of contents of cell; (do not allow “resistance of cell”)

the emission of electrons from a (metal) surface by photons/light/electromagnetic radiation (incident on the surface);

(i)     caesium electrons are less firmly bound / mercury requires more energy to release electron; } (allow reverse argument)

If answer is in terms of threshold frequency, frequency must be linked to energy via \(E = hf\).

(ii)     energy of photon \( = \frac{{6.63 \times {{10}^{ - 34}} \times 3 \times {{10}^8}}}{{2.1 \times {{10}^{ - 7}}}}{\text{ }}\left( { = 9.5 \times {{10}^{ - 19}}{\text{ (J)}}} \right)\);

convert photon energy to eV, 5.9 (eV) / convert work function to joules \(7.2 \times {10^{ - 19}}{\text{ (J)}}\);

so kinetic energy of electron = (photon energy \( - \) work function =) 1.4 (eV) or \(2.3 \times {10^{ - 19}}{\text{ (J)}}\);

Award [3] for a bald correct answer.

(Schrödinger model suggests) electron is described by wavefunction;

that gives probability of finding electron at a particular place / probability of finding electrons is proportional to square of (wavefunction) amplitude;

so position of electron is uncertain;

(i)     Superficial answers were common. Candidates continue to ignore the mark allocations for questions and therefore misunderstand the number of independent points they should mention in an answer. Here, most said that conductors contain free electrons (or the reverse for insulators) but did not go on to discuss the role of the free electrons in carrying charge or to relate the current to the existence of an electric field across the conductor. Far too many gave answers of the “conductors conduct well” variety that do not score marks.

(ii)     Too often candidates were content to suggest that the internal resistance of a cell is the resistance of the cell contents without discussing the physical implications of this. It was rare to see a consideration of the energy dissipation in the cell or an explanation of the way the power loss is related to a “resistance”.

Many candidates were able to give a complete description of the photoelectric effect.

(i)     Although the majority were able to relate work function to the physics of the electrons in the metal, some could only respond in terms of the minimum frequency required to produce a photocurrent. This did not generally score marks without some supporting remarks.

(ii)     Generally, candidates were able to score at least two marks. Work was marred by power of ten errors and by inabilities to convert between the electrovolt and the joule. A major reason for errors was that candidates often did not begin with a clear statement of the photoelectric equation followed by substitution in an organised way.

Significant numbers scored two out of three marks. There were some good attempts to link the wavefunction idea to the probability ideas of the theory.