The technical questions really depend on who's interviewing you. They know that people's knowledge of electronics is going to vary a lot and so I don't think they'd ask anything that you couldn't answer on it. From what I remember, most people were asked various questions about the areas of maths that they were studying. I was asked to talk generally about decision maths, which was horribly open-ended but wasn't too bad in the end.
Keep in mind that they're not trying to see whether you can do various bits of algebra and remember physics equations - that's what the exams are for. Rather than a formal assessment, they're just trying to see how you approach the problems that they give you and how you can explain what you're doing. If you can't do the problem it's not the end of the world as long as you can try to tackle it intelligently.
In any case, I wouldn't be too worried. The technical part is only half of it, and the interviews are not a proper academic assessment, rather just a way to make sure you're suited for the course - which, if you're enthusiastic about it, shouldn't be a problem.
Good luck!