Will I have to teach other subjects apart from physics?

The short answer is: almost certainly in Key Stage 3, maybe in Key Stage 4 and in exceptional circumstances post-16.

The long answer involves looking at individual schools and individual teachers within them. It also depends on what subjects you choose to train in.

Please note that physics with maths is currently only available as a PGCE option. If you are considering school-based training, you would usually train as a science teacher but check with individual providers.

At A-level, it’s likely that you will not teach chemistry or biology. Schools are more likely to have specialist teachers in these subjects than in physics so your time will be dedicated to teaching physics. 

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. So actually chemists and biologists are more likely than physicists to have to teach outside their subject specialism.