Knowledge of scientific principles is also mandated as a result of a need to understand best and safest practice, especially in the use of ionising radiation where legislation, guidance and risk all form part of a medical specialists' pressures at work. It is no surprise therefore that radiologists are obliged to study and pass physics exams. Such exams can present a considerable challenge and the authors of this work recognise and sympathise with that challenge and have created a volume which is intended to be an educational resource and not just a pre-exam `crammer'. Both authors have considerable experience in teaching, supporting and examining in medical science and have developed an awareness of where those sitting professional exams have traditionally struggled. This text is a distillation of that experience.