When it comes to saving energy, there are a bunch mistaken assumptions that often mislead people and cost them more money. The very vexing thing about these energy misconceptions is that, at first glance, they make seem to sense — until you examine the facts.
In our final installment of the “Challenging Common Energy Misconceptions” series, we want to examine some energy facts so odd that they couldn’t possibly be true — but they are.
1) Power your gadgets with fruit.
You can use a lemon to make a wet cell battery using a penny and a galvanized roofing nail. Yes, this is a classic science fair experiment, but if you start thinking about the number of low-voltage devices in modern life (like cell phones), it’s really tempting to think about what you could power with fruit or potatoes.
Of course, the voltage and current output from fruits and veggies are so low (.9 volts and 240 microamps (µA)) it would take three or four to illuminate a single LED light. You would need a huge array of fruit wired together to kick out the 5 volts at 2.4 amps to power a cell phone.
Curiously enough, this is the same hurtle Alessandro Volta encountered when he developed the first electro-chemical (wet cell) battery in 1799. Termed a Voltaic Pile, you simply stack alternating layers of copper, card stock, and zinc and surround them in a solution of brine as an electrolyte. The electro-chemical reaction (oxidation and reduction) gives off an electrical charge and hydrogen gas. The more efficient the electrolyte at moving along the reaction, the more powerful the battery. In fact, car batteries are wet cell batteries that use highly corrosive sulfuric acid and lead.
Now, who wants to start squeezing some citrus so I can start charging my smartphone?
2) Need a resistor? Just draw a line on some paper with a pencil.
Resistors are a basic electronic component that reduces the flow of current. Most are made of carbon, and their resistance is measured in ohms. The more carbon, the higher the resistance and the less current that gets through the circuit.
Pencil lead is actually carbon graphite and it does conduct electricity. If you draw a line on a piece of paper and check the resistance with a multi-meter at increasing distances, you will discover the resistance increases as the probes get further apart.
The same principal holds true even for excellent metal conductors because they all resist electrical current to varying degrees. Steel may do a great job of conducting electricity, but if you’re transmitting current over hundreds of miles, the natural resistance of that amount of steel will add up and reduce the amount of current at the end of the line — just like the pencil line does. In the electricity transmission business, this is called “line loss”.
Now, if you could draw resistors, wouldn’t it be cool if you could just paint surfaces with conductive material to turn them into a switch or sensors? Guess what? You can!
3) Hold a fluorescent light tube over your head under a high voltage transmission line and the tube will light.
High voltage alternating current (AC) in transmission lines produce electric fields. This field can be strong enough to excite the electrons of the mercury vapor inside the fluorescent tube and cause them to glow. Ground-level electric fields under a line might be as high as 10 kV/meter depending on the transmission line voltage.
In fact, all wire carrying AC give off an electric field. this can be shown by laying a fluorescent tube across the wires to sense it. Holding one in your hand while rubbing your feet on a carpet to build up a static electric shock will also cause it to glow.
While wireless power transmission resonant energy transfer is nothing new (explored by Nikola Tesla a century ago), making it practical and safe has been somewhat illusive. That’s starting to change with differing technologies using radio frequencies or magnetic fields to wirelessly charge devices several feet away. Apple, a company named for a fruit that can also be used as a battery, has been cautiously interested.
Hopefully, you’ve enjoyed our “Challenging Common Energy Misconceptions” series as much as we’ve loved writing it!