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Funny you should ask quibbles

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1371624.  Wed Jan 13, 2021 5:36 pm Reply with quote

Dear QIites and elves,

"Funny you should ask" is my favourite downstairs loo book at the moment, and much I have learnt. However, a couple of quibbles...

1) p 118 refers to citric acid as being bitter. Citric acid is not bitter, but is sour. It is oils in oranges that makes them bitter. Worth also mentioning to be careful when zesting oranges, as the oil present in the zest will dissolve a number of plastics... Ask me how I know...

2) p185 "Quartz is useful to watchmakers because of a curious property it has: when you run an electric current through it, it vibrates backwards and forwards, 32,768 times a second."

I'm sorry dearest elves, but this just isn't true. Crystal oscillators used in watches, phones, computers etc contain tiny quartz tuning forks which are carefully manufactured to be exactly the right mass to oscillate at 32,768Hz (or as close as possible). Other frequency quartz oscillators commonly used are: 2.88, 3.072 and 3.088 MHz. It's a result of the manufacturing that gives a frequency of 32,768Hz, not something inherent about quartz.

The reason they are manufactured to resonate at this frequency is that 2 to the power of 15 is exactly that number. A digital watch has a row of 15 flip flop circuits, the output of each flip flop is the input of the next. This is a cheap and easy way of counting up to 32,768. When the "most significant" flip flop is triggered, exactly 32,768 oscillations of the crystal have occurred, and because the crystal is vibrating at 32,768 oscillations per second, exactly one second has passed.

The watch manufacturers could use one flip flop less, and a crystal that oscillates at 16,384Hz, but to young people able to hear up to ~20kHz, the watch would make a quiet high pitched whine which would be annoying when resting or sleeping. 32,768 is the lowest power of 2 allowing use of a crystal oscillating beyond the range of human hearing. Might annoy your dog though!

There is an excellent video covering this topic in much detail here:

Much Love


1371698.  Thu Jan 14, 2021 10:44 am Reply with quote

Hi Olly and welcome to the forums. We love a good quibble, and that looks like a good one. Thank you!


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