The physics of making a cup of tea

St John’s Physics Tutor Professor Tony Weidberg loves a good cup of tea, so why not make yourself a brew and have a go at his physics brainteasers…

Q: At the interval during a football world cup game, some people watching at home make a cup of tea using electric kettles. Make a reasoned order of magnitude estimate of the load on the national grid. Note there is no “correct” answer.

Q: You make a cup of tea using boiling water. You will add milk at some point before you drink it. You need the temperature to drop below some limit in order for it to be comfortable for you to drink it. Should you add the milk at the start or just before drinking the tea?