Yesterday, we ran a video showing you a water powered battery that can generate a 15kV spark using nothing more than some simple hardware and a professor who looks a bit like Einstein. Some readers may have worried that it was a spoof given the date (April 1) but this is a genuine piece of science based on the principles of static electricity.
Water is a polar molecule – there is a small difference in electric charge from one end to the other – but pure (deionized) water is also a very good insulator. As the droplets of water fall through the bottomless metal cans, their polarity induces a charge in the cans (which are by the way heavily insulated from earth (or ground). A positive charge builds up on the cans as the water molecules falling into the buckets become negative. This results in a charge separation or a potential difference between the paint cans and the buckets of water (which are also heavily insulated from earth).
Eventually the potential difference reaches a threshold at which point the insulating properties of the air between the two balls breaks down and a spark leaps across the gap. This spark, which has a temperature of several thousand degrees Celsius carries a voltage of between 10 and 15 thousand Volts, far more than you need to power even the biggest set of plugin speakers for your mp3 player.
Several questions remain. Where does the energy come from to create this enormous potential difference and could this form of electricity be tapped by building some kind of power station at the top of a waterfall and using two enormous cans and buckets? Well to answer the first question just look at the vertical arrangement of the equipment. The energy comes from gravity, from the potential energy of the water, which is above the paint cans. The second question is a little more complicated to answer. It would be possible to build a bigger generator, although insulating the components from earth would be tougher and the dissolved salts in river water would make it far less efficient than a generator using deionized water, but those are probably not the main issues.
Think about it, to make electricity generation useful we need a current to flow. How might you “tap” off a current from this type of generator when its product is effectively small-scale lightning? A capacitor in the spark zone, you say? But then isn’t the air acting as a capacitor, still doesn’t solve the problem of tapping off a current. Find an efficient and safe way to tap the power of lightning and you could make a fortune and solve the world’s energy needs. But, please don’t try those kinds of experiment at home!
Instead of generating static electricity, however, it is possible to use gravity’s power to move water to produce a current, much more readily…think water wheel, dynamo-type generator…think hydroelectric dam.
By the way, this experimental setup was originally devised by Lord Kelvin in the nineteenth century and is known as Kelvin’s Thunderstorm, it featured in Bill Beaty’s amateur scientist column in 1995, you can find a more detailed explanation there.
This isn’t exactly your average high school science fair project, in fact please don’t try this for yourself without proper supervision, as you’ll need a magnet, a chunk of high temperature superconductor and a flask of liquid nitrogen, oh and a pot that won’t crack when you pour in the liquid nitrogen. (Standard cyro lab safety equipment is recommended) When this video first hit the streets, lots of people said it was a fake, but what it is, is a classic demonstration from modern physics of non-classical behaviour in materials cooled below a certain critical temperature. The effect in question is well-known to scientists working with superconductors and is known as the Meissner-Ochsenfeld effect, or more commonly the Meissner effect. Poor old Ochsenfeld rarely gets a name check. It was discovered by the pair in 1933, so it’s nothing new to physics, relatively speaking.
Have you ever been stuck for AAA batteries? You know those skinny kid brothers of the AA 1.5 volt you use in your mp3 player? No? Well, this guy obviously has. But, unbelievably what he wasn’t stuck for was a 9V battery and a pair of sharp-nosed pliers. So, with a handful of dead AAAs and no battery store for miles, he hacks open the 9 volter and pulls out six skinnier still unmarked batteries, which he refers to as quadruple A (AAAA) batteries.
Everyone who studies any science at school will have come across Newton’s Laws of Motion. His three physical laws explain the relationships between the forces acting on a body and the motion of that body and were first published in 1687 in his magnum opus – Philosophiae Naturalis Principia Mathematica.
By definition the use of significant figures in measurement and value is a form of rounding. They represent the the number of digits in a number, beginning at the first non-zero digit and including any trailing zeros. For instance, 0.005746180 has 7 significant figures. All 7 of those digits are significant, if someone were measuring a distance, volume, time period or whatever and they included all those numbers as well as that final zero, you would assume that they had measured the value to seven significant figures. The next number after the final digit would not be reliable and so is not included.
“Can visible light ever be manipulated so that it bends the wrong way?” asks Katharine Sanderson in Nature. She suggests that successfully reversing light by making a negative refraction material could open up the possibility of some rather futuristic devices, such as microscope lenses that can resolve objects smaller than the wavelength of light or the much-desired invisibility cloak.
Ever fancied squeezing an egg into a bottle? No? Well, it’s a kind of perennial physics demonstration that science teachers the world over love to do. I could simply describe how to do it and the results you might expect, but that would be no fun at all. Instead, I spent a good ten minutes scanning videos on the net where individuals attempted to carry out this experiment, some of them more successfully than others. Most handling naked flames and solvents (methylated spirits and the like) in a non-laboratory setting with absolutely no safety equipment (not even goggles) in sight.