Touch switches, unlike normal switches, have no mechanically moving contacts. There are several ways to make them.
One is to have two bits of metal close together that you need to touch. Your finger isn't that bad an electrical conductor, and it connects the two. A newspaper is a bad conductor and wouldn't connect them.
Some switches are made that rely on heat from a finger or on changes in (possibly infrared and thus invisible) light reflected from them. These are often used in public washrooms to turn water on and off at a sink without the need for physical contact with a faucet. Such switches are often a bit awkward to use reliably.
Your lamp that needs a human touch to go on or off is probably based on your being, to some approximation, a big lump of conducting material - something like a big lump of metal.
Since you're like a big lump of metal, you're also like a big antenna. Whether you notice it or not, you are picking up all sorts of electrical noise (unavoidable in our environment) and when you touch the lamp, that signal is picked up and is interpreted as the switch being "pushed."
Another way it might work is based on the fact that every lump of metal has a property called "capacitance" which measures how easy it is to put electrical charges on it. As you might imagine, it's bigger for big objects than for small ones. The idea here is that when not touched, the capacitance of the (small) thing you touch is very low, and increases dramatically when you (acting as a big lump of metal) connect yourself to it by touching it.
So, hitting the lamp with a newspaper won't work. You might, however, get results hitting it with a sheet of aluminum foil!
Dr. Knowledge is written by physicists Stephen Reucroft and John Swain, both of Northeastern University. E-mail questions to drknowledge@globe.com.
