My physics oral exam at the ENS: "Have you seen videos of supraconductors levitating above magnets? 1. Prove that they do levitate. 2. If a supraconductor levitates for 30 min, estimate an upper bound for its resistivity." 1 hour exam at the blackboard, no preparation, no documents, no computer or calculator, no pen or paper... just you standing alone with a piece a chalk and a top physicist staring at you. Supraconductivity wasn't even part of the program. The whole point was to figure out a decent model and derive everything from first principles (ie Maxwell equations, which you were supposed to know by heart, alongside approximate values of the universal constants). Note: my specialty was math, not physics. I can't even imagine what the questions were Iike for the physics students.
