i got asked mainly just pure maths an pure physics stuff...
calculus, graphing equations, capacitance, force extension graphs, errr, stuff like that! brasenose college gave me a pre-release type thing, basically an article about fuel cells and then i got asked like 2 easy questions about that
my advice: be curious about things, it shows ur interested, and if they ask you something you haven't done, say you haven't, then go on to take an educated guess, it shows u can think outside your box (i hadn't done integration by parts, and he asked me to derive it from the product rule!)