What will grade boundaries look like for an A and A* for the new spec AQA A level Physics Paper? Will they be lower than the past, or similar?
Last year on the new spec AS physics paper it was 64% for A. Based on that, I would say 75% for an A* and 65% for an A. I would assume an error bound of +/- 2 or 3%.
How should I revise? Past papers, what else?
72% is great! You're only 3 or 4% off an A*. Unless something really bad happens, you should get an A easy. Question: What did you get for your A2 mocks?
The reason why our new exams are linear and really hard is because of Michael Gove.
I want to study engineering.
The answer to your question is to do both.
Do questions topic by topic but ONLY on topics you struggle with. For example, I find EM induction (especially Lenz's Law) the hardest topic in A level physics.
Do say, 3 past papers, mark them and see if there is a specific topic which you struggle on. Revise the topic using a book or videos then do specific questions on that topic from physics and maths tutor.
I remember seeing many people on TSR after as level paper 1 last June saying that they did all of the old past papers, but it didn't help.
If you see a really hard question you can't do, I would skip it, and come back to it later. You'll look at the question in a different light and it will just click.
When you drop a magnet down a tube, the copper tube cuts the magnetic flux lines created by the magnet so an emf is induce. Because the tube is a complete circuit, a current flows through the tube. This current will then induce a magnetic field of its own.
Now, lenz's law states the direction of the induced emf will be in such a direction as to oppose the change in magnetic flux that created it. The change that induced the emf is the manget falling down the tube. Because of this, induced magnetic field will be such a direction as to repel the falling magnet upwards.
The magnetic creates electrical energy in the pipe, but the current in the pipe creates a magnetic field that slows the magnet down. For every 1J of electrical energy created in the pipe, the opposing magnetic field causes the magnet to lose 1 J of kinetic energy. That is is how Lenz's law works: if the induced current didn't flow in such a direction as to oppose the falling magnet, energy would not be conserved.
Don't ask me why the current reverses direction after the magnetic falls half way through the tube; that answer involves 1st year university physics.
I don't understand what your second question. Suppose Lenz's law doesn't exist. In order for there to be ever increasing flux that magnet would have to fall through that rube for ever. This would not happen; the flux linkage in the copper tube would stop once the magnet fell out. Could you support your question with an example?