AQA A-LEVEL PHYSICS 7408/2

AQA A-LEVEL PHYSICS 7408/2 Question Answers Additional comments/Guidelines Mark AO 01.1 28 (°C) 1 01.2 The energy transferred reduces the number of nearest atomic neighbours OR allows atoms to move their centre of vibration OR breaks some of the (atomic) bonds OR crystalline to amorphous (owtte) First alternative must not imply total loss of intermolecular forces or neighbours. A reference to ‘breaking the bonds’ implies all the bonds and does not gain the mark. No mark for saying bonds weaken. However these errors in discussing the bonds does not prevent a mark coming from another point Last alternative might be expressed as ‘atoms change from fixed positions to them being able to slide around each other’. Ignore any references to changes in separation. An explanation that involves increasing the kinetic energy will lose the mark. So will any description that implies it becomes a gas. 1 01.3 The (total or mean) kinetic energy remains constant. The (total or mean) potential energy increases. 2 01.4 The mean speed/mean kinetic energy increases Ignore references to larger separation (because it’s not always true): collisions (as it is not a gas) or measures of randomness (which are usually too vague). Condone use of average for mean. Don’t allow velocity instead of speed. During this time interval the atoms are all in the liquid form so no credit for references that indicate a change of state. 1 01.5 Using both ∆Q = mc∆θ and ∆Q = P∆t (c = P∆t = 35 × (14.8 − 11.2) × 60 = 369) m∆