The only notes that you are allowed in the Foundation exam is the 4-page exam booklet (Link: EX307 PDF)
The exam Invigilator will check to make sure that you have not added any notes of your own, and that you have no other material that you can refer to. Using other notes, study material, books, Google, etc, will disqualify you.
Once the exam has started though, you can use a sheet of blank paper, or write on the the EX307 booklet if you need to jot something down or draw out the Ohm’s Law triangle… but only once the exam has started.