Science: Technoquest

Q: Why do batteries that are running down recover slightly if you don't use them for a while?

In a copper-zinc battery, a copper plate and a zinc plate sit in a dilute sulphuric acid solution. When the battery is working, small bubbles of hydrogen gradually form around the copper plate and prevent the flow of charge. When the battery is disconnected, some of the hydrogen disperses slightly. When you use the battery again, there is less hydrogen to block the flow of electrons, so, for a short while, the battery will work again. Then the hydrogen builds up, and again the battery fails to work.

Q: Who invented the fountain pen?

When pens were first invented, the nib had to be frequently dipped into a container of ink. This slowed down the process of writing considerably. As a result several people had the idea of creating a pen where the reserve of ink was attached to the pen. The first working version of such a pen was patented by LE Waterman in 1884, in the United States.

Q: What's the device in an infrared burglar alarm detector called, and how does it work?

The device which does the detecting in a burglar alarm is called a pyroelectric sensor. It consists of a number of crystal elements (usually lithium and antalate) which are sensitive to infrared energy and convert it into a small electrical signal (usually about 200 micro-volts). This signal is used by the rest of the device to trigger the alarm itself.

Q: What happens to the waste from a lavatory on an aeroplane?

It is all stored on the plane. It is a myth that it can "leak" out and fall to the ground. The bits of ice that can fall from a plane generally come from the wings of the plane, where ice builds up from water vapour in the clouds.

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