Hi there, my kid got a place on the PhysNatsci course. His primary interest was in physics, but he has now got really into chemistry since he started it. This is what I advise: First of all, sign up for the Isaac Physics Mentoring Scheme here:
https://isaacphysics.org/pages/isaac_mentor. Also, once you are registered on Isaac Physics, make yourself do some Isaac Physics, Maths or Chemistry every day (but you are allowed to have one day a week off
) for ten or even twenty minutes.
Secondly, read widely on subjects that specifically interest you. I recommend perhaps avoiding cliched popular scientists like Brian Cox, because I expect Admissions Tutors remain unimpressed when he is mentioned in anyone’s statement. There is the really excellent and genuinely informative book, Why Chemical Reactions Happen by Wothers and Keeler (Wothers is at St Catharine’s and Keeler is at Selwyn, if you are going to get an interview at either college, it is likely you would be interviewed by one of those two learned Professors, they are both very charming). For other book ideas, look through the recommended reading lists from both Oxford and Cambridge Colleges, and perhaps some US universities and chose stuff aimed at people who are in Year 12 or Year 13 under university age rather than unintelligible First Year texts.
Watch lecture series on YouTube like this one by Leonard Susskind:
https://www.youtube.com/playlist?list=PLQrxduI9Pds1fm91Dmn8x1lo-O_kpZGk8 or any others that take your fancy.
when you get your interview you will need to demonstrate a high level of skill in maths, preferably in further maths. This will underly all the interviews you have even the physics and chemistry, so try very hard with maths and do everything you can to make sure there are no holes in your maths, if you shine in your maths, this will serve you very well.
My son was really interested in astrophysics and joined a local society and attended weekly meetings which he thoroughly enjoyed, even though he was the youngest one there. He also attended three Masterclasses in Cambridge and did a Sutton Trust summer school. A summer school at any university in Chemistry or physics will serve you well. Imperial offers these as well as Cambridge and Oxford. He also attended the Cavendish Laboratory 6th Form Physics Lectures, perhaps those will be online this year?
Your statement should explain Clearly, enthusiastically yet concisely what you learned while doing each of the above, when you say that you did something, also explain what you got out of it. Your statement does carry quite a lot of weight because there will be lots of statements to read so they need to be non-cliched ones that are authentic and stand-out from all the ones droning-on about Stephen Hawking, Einstein and Brian Cox (although all three were/are great people).
It is a big effort to prep an application for Oxbridge and very much worth the time – you are great because you have started to prepare early and you have sought out other people’s advice. I wish you all the very best of luck and hope you will come to Cambridge one day.