Doing a test may not be your idea of a cool holiday activity but CGP (the publisher of your revision guide) has just released a series of free online GCSE tests that I highly recommend.
You can access the tests at https://www.cgpbooks.co.uk/resources/free-gcse-science-10-minute-tests. On the landing page, select Separate Science then choose Physics. You will have 10 minutes to answer up to 50 multiple-choice questions. All the answers are given at the end, together with brief explanations that identify the reason for each correct answer.
In case you are interested, the question I got wrong concerned the UK domestic supply voltage, for which I selected a value of 240 V. The correct answer, as I’m sure you know, is actually 230 V.
In my defence, I used to work in the electricity industry and I remember when the UK voltage was 240 V. At this time, the rest of Europe was on 220 V. As part of European harmonisation, it was decided that all of Europe, including the UK, would use the same voltage but nobody could agree on which voltage would be used.
The decision was taken to standardise on 230 V. You might think this was the perfect compromise since nobody had won. But things weren’t quite that simple. As I recall, the specification came with a tolerance, which was +/-5%. If you do the calculation you will realise that 5% of 230 V is equal to 11.5 V, meaning that the allowable voltage range was from 218.5 V to 241.5 V. This range encompassed the UK’s 240 V and Europe’s 220 V, so neither the UK nor mainland Europe had to change its supply voltage in order to comply with the harmonisation directive.
Things today are different and 230 V is indeed the domestic supply across Europe but it still amuses me to think back to the voltage change and the politics of compromise that it embodied so brilliantly. And occasionally I forget that 240 V isn’t actually right any more!
Mr Tarrant's physbang 'blog 