Physics (or science) PGCE
The traditional training route for physics teachers is that you specialise as a physics teacher whilst also preparing to teach chemistry and biology.
Whether or not you teach outside your specialism depends on your particular circumstances and decisions, but here is the general picture.
The National Curriculum combines physics, chemistry and biology into ‘science’ at both Key Stage 3 and 4. At Key Stage 3, most – but not all – schools use science teachers to teach across the science curriculum.
At Key Stage 4, pupils sit for a single, a double or a triple science award at GCSE. Those taking the triple award are most likely to have specialist teachers at KS4 as they are usually taught the three subjects separately. If they can, many schools will also use specialist teachers for pupils sitting the double award.
At A-level, you will almost certainly not teach chemistry or biology. The sad fact is that physics suffers from the greatest shortage of specialist teachers and 500 maintained schools in England alone do not have a physics specialist.
Schools are more likely to have specialist teachers in these subjects than in physics so your time will be dedicated to teaching physics.
So actually chemists and biologists are more likely than physicists to have to teach outside their subject specialism.