electricity and entropy
Outline
- static electricity is built-up charge
- like poles repel; opposites attract
- magnetic attraction has practical uses
- electricity flows through a conductor
- energy changes, becoming less usable
- an electric motor uses magnetism
- things wear down unless kept up
- resistance acts to oppose flow
- measurement affects what is measured
static electricity is built-up charge
Fall Fashions, Static Spark, and Dust Magnets
Maple Lane, where neighbours hold their community garage sale, is so named for the many sugar maples and other colourful deciduous trees. This autumn, with strong sunlight and cool dry nights, the leaves are brilliant red.
After summer solstice, with less light each day, the maples pull nutrients back into their trunk and roots. The leaf stops producing the green pigment chlorophyll, revealing splotches of red and yellow.
The cool, dry weather is also ideal for static electricity, both big as lightning and small as sparks. Friction between shoes and a nylon carpet can cause static electricity to build up on a person, although static spark is less likely on humid days. Moisture in the air neutralizes the charge.
Static electricity makes clothes cling and produces in a small spark when metal is touched. This spark or discharge is, in fact, miniature lightning. That is, finger sparks and lightning are static electricity.
Clouds become charged as ice crystals inside them rub against each other. The build-up eventually cannot be held in the cloud and a flow along the path of least resistance is found as a bolt of lightning.
Static sparks can occur between clothes coming out of the dryer, or by taking off a sweater on a dry day. Static cling can also hold a balloon to a wall after the balloon is rubbed on a person’s hair.
Static electricity can be harmful to sensitive electronic equipment, such as repairing a computer circuit. It can be dangerous during surgery if a heart or other sensitive organ receives the spark. In fact, trucks carrying flammable cargo used to drag chains to discharge static electricity built up by friction with the air. Now, the tires for trucks carrying flammables are made with metal strips built-in.
Lightening that hits the ground can travel up one leg and down the other, leaving a person temporarily stunned. The further apart the legs, such as with a cow, the greater the amount of current across the body. Lightning that strikes near a house can even enter through the plumbing system, so it is best to wait on a bath until the storm passes.
During a lightning storm, don’t stand under a tree or touch an automobile. However, it is safe to be inside an automobile. The metal body conducts electricity, so the current stays on the outside. A metal airplane likewise protects passengers once aboard the plane.
Static electricity is useful in spray-painting metal objects, such as auto parts or patio furniture. The positive paint, attracted to the negative metal like a magnet, covers in one coat with no dripping.
A photocopier is similar. Parts of a rotating drum are charged to attract the powdered ink toner. Paper passes through, picks up the toner by static cling, then heat melts the toner into the paper.
An electrostatic air purifier is a magnet for dust in the air. Particles flowing through the filter are given an electric charge. They are then attracted to the magnetic plates in the purifier.
likes poles repel; opposites attract
Pole to Pole, Iron Fortified, and Cooking by Friction
Iron is in bridges and buildings and blood. Iron helps carry oxygen in red blood cells, for instance. Some breakfast cereals are fortified with small bits of iron. Breakfast for Clay is often a bowl of cereal, packed with vitamins and fortified with iron.
CLAY
A magnet will attract iron. If iron is in my cereal, my cereal must be magnetic.
The iron in dry breakfast cereal is the same mineral as in a cast iron skillet. In the digestive tract, iron changes into a form the body can absorb and use. A strong magnet can pull the iron out of cereal fortified with iron.
Magnets have a north pole and a south pole. Break a magnet in half and each half becomes a magnet. The Earth is a magnet, with north and south poles. An atom is a magnet: negative electron, positive nucleus.
Opposites attract. The north pole of one magnet will attract the south pole of another magnet. But a magnet will also attract metal that is not a magnet. Iron, for instance. Both poles will attract the iron.
A magnet sticks to iron by making it a magnet. The north pole makes an iron bar temporarily into a south pole and attracts it. The south pole makes it temporarily into a north pole and attracts it.
Some animals use magnetism to navigate. Pigeons and Monarch butterflies, for instance, produce grains of iron magnetite. They use magnetite with the Earth’s magnetic field to navigate, like a tiny GPS.
Opposites do attract, yet north on a compass points north. That’s because north on a compass is really the south pole part of a compass needle, painted to look like it is showing Earth’s north pole.
Water is hydrogen and oxygen. H2O. A water molecule is a small bar magnet: negative on the oxygen side; positive on the hydrogen side. A microwave uses water like bar magnets to warm food by friction.
A microwave oven sends a magnetic wave into the box where food is placed. The water molecules in the food flip to line up with this magnetic field. The wave, however, keeps flipping back and forth.
As the magnetic field flips, water molecules in the food flip to keep up. Two and a half billion times every second. Food heats up by friction between flipping water molecules and the rest of the food.
Paper and glass have little water, so they don’t heat up in a microwave oven. Popcorn has moisture in the kernel that heats up and busts open, sending a sound wave with a characteristic pop, pop sound.
An ice cube has a lot of water, but frozen—fixed in place. As a result, a microwave oven does a poor job heating up ice. Metal reflects microwaves, which could cause damage or even a fire in the oven.
magnetic attraction has practical uses
Magnetic Images, Household Uses, and Finding Poles
Lark works in the imaging department of the local hospital. One device in her department is the MRI or magnetic resonance imaging machine. A patient lies in a tube and surrounding magnets align water molecules in the patient’s body. Radio waves then pick up signals and create detailed images in slices, like slices of bread.
At home, Lark finds magnets all around. In cabinet door latches and audio speakers. On credit card stripes and purse snap closures. In motorized devices from electric toothbrush, to cordless drill, to garage door opener.
Karl has a variety of uses for magnets in the garage, especially the strong neodymium magnets. Using a hot glue gun, Karl stuck disc magnets on the wall. Now they hold up pliers, hammers, clippers, or any metal tool. He puts one neodymium magnet on a screwdriver so it will pick up and hold screws in place. It works. With another magnet is his shirt pocket, screws and nails stick to the outside of his shirt for easy access.
When Karl spilled a box of nails, he held a neodymium magnet on the bottom of a cardboard box and turned the box upside-down over the spilled nails. The nails jumped up, back into the box.
To clean the inside of a fish tank, Lark borrowed an idea from the surgery team. Surgeons use powerful magnets outside a patient’s body to guide instruments and perform procedures with fewer incisions.
Lark put a neodymium magnet in a sponge and put the sponge into the fish tank. Using another magnet on the outside, she moved the sponge around, scrubbing the tank without disturbing the fish.
Doing maintenance work, Karl developed an appreciation for the properties of shapes. Maintenance hole (manhole) covers are round, for instance. That is so they can’t be accidentally dropped into the hole.
A torus (donut shape) could be turned into a single-handled coffee cup without tearing or punching. They both already have a hole. A cube could be turned into a cylinder. But a cube cannot be turned into a torus without tearing or punching.
So a horseshoe magnet is equivalent to a bar magnet by shape and by having north and south poles. Both are equivalent to a spherical magnet. Lark picks up an orange and tries to imagine it as a magnet.
KARL
Think of it this way: when the wind is blowing, there must be another place on the globe where the air is still.
Magnetic flow around a sphere also has an origin and destination: the poles. Every magnet has two poles. Even a sphere like the Earth has two magnetic poles. Put a couple magnetic spheres together and they will align to attract north to south poles. Sphere magnets stack easily.
electricity flows through a conductor
Electro-Quiz, Brain Sparks, and Ohm Lying
Home-made gifts are a tradition in Mona and Noam’s family. With the holiday season coming up, Lacy made a family-history quiz for her grandmother. First, she wrote questions on the front of a manila folder.
Lacy taped aluminum foil strips inside, connecting choices with answers, punching holes beside each. She put paper clips at both ends of a length of bell running along a small bulb and battery.
Touching one paperclip to a question and the other paperclip to the correct answer completes a circuit and the bulb lights up. Of course the manila folder is taped closed, so grandma can’t see inside.
With a correct question to answer connection, the bulb lights up. It lights up right away, although electrons move through the copper wire about as fast as an ant walks, one centimetre each second.
Electrons move at the speed of an ant, but the pulse of an electrical signal moves along the wire at nearly the speed of light. In one second, the pulse could go around the Earth’s equator seven and a half times.
Paper is an insulator. Lacy put paper tape between the foil strips to prevent short circuits. In a short circuit, the electrical pulse would take the shortest route rather than the intended route.
The battery is rechargeable, but it seems to take a little longer each time to recharge. It’s that way with the battery in her smartphone and electronic tablet. Fast to partially charge; slow to fully recharge.
Rechargeable batteries charge quickly at first, but take much longer to finish fully charge. They are like suitcases in that sense. The fuller it becomes, the harder it is to add more and the longer it takes.
As Grandma tries out a lot of different choices, the wire becomes warm. Most of the electrical resistance is in the wire. Power lost due to resistance is converted into heat, such as the coils in a toaster.
The longer the wire and thinner it is, the more the resistance. It is like watering the garden through a long straw. The water has a harder time passing through. Shorter and wider, less resistance, like a fire hose.
Lacy’s brain is a bit like this. Impulses travel along nerves as an electrical wave, although they ferry across from one nerve to another by means of chemicals. Her brain produces 10 to 15 watts of power. That’s about as much as a single LED light bulb uses.
A lie detector is similar to the manila folder quiz, but with sweat for aluminum strips. When a small voltage is applied, a sensitive meter shows whether current flows across the skin when a person sweats.
Lying promotes perspiration. Perspiration consists of a salty water solution, which is a good conductor. Better conduction (lower skin resistance) results in a higher meter reading.
Lie detectors aren’t very reliable, however. Some liars don’t sweat under pressure and other people telling the truth do. Even nervousness of taking a lie-detector test can give a false reading.
A lie detector used by some poker players is dilation of the pupil. Look into the eyes of an opponent to detect a bluff. Contracting pupils suggest that a person is displeased with what he or she senses.
as energy changes, it becomes less usable
Magnet Train, Heat Change, and Things Deteriorate
As a present for Clay, Lacy made a train out of neodymium magnets, a AA battery, and bare cooper wire. She tightly wound a length of the wire around a wooden dowel to make a long coil a little larger in diameter than the diameter of the battery.
The magnets are discs, the same diameter as the battery. Lacy put one magnet on each end of the battery, north poles touching the battery. The train is made of disc+BATTERY+disc.
Put the train inside the coil and it immediately begins to moves along inside the coil from. It moves from one end to the other, or will go around and around without stopping if the coil is bent into a circle.
The magnets touch the coil and create a circuit from one end of the battery to the other. This creates a magnetic field around the wire that repels a magnet on one end and attracts a magnet on the other.
Electricity flows in the circuit, which means the train will keep moving until the battery runs out. The AA battery runs out when the chemicals inside break down, unless it is a rechargeable battery.
A battery recharger reverses the flow of energy using a power source, such as solar panels. Energy cannot be created or destroyed, only change form. A solar panel changes light energy into electrical energy.
Household electricity comes from the flow of water through a dam. Water turns a turbine, which generates electricity. Coal, wind, and steam can also be used to turn the turbines that generate electricity.
Things deteriorate, becoming less usable, less organized. Batteries run out. Lacy’s room goes from clean and tidy to a bit messier each unless put back in order. A car runs out of gas. A campfire dies out.
To make it usable again or restore order, energy has to be put into a system. The battery has to be recharged; Lacy has to clean up her room; the car has to be filled up; the campfire needs more wood.
Heat flows from warmer to colder unless work is done to reverse it. For instance, an air conditioner to offset summer heat. A furnace in winter to replace heat lost through windows and doors.
The universe as a whole is like Lacy’s room. Energy can be converted, but some is lost as waste heat. The amount of disorder or waste heat builds up. It is not possible to get more energy out of a system than is put in.
As Ajay knows from his cabin, you can’t cool off a room by leaving the ’fridge door open. More heat is given off by the motor than is absorbed by the released cool air; the room becomes even warmer.
an electric motor uses magnetism
Mini Mags, Rowing the Boat, and Making a Motor
Lark bought a strip of flexible magnetic tape for crafts and fridge magnets. She cut it in half. Both halves have north and south poles and are magnets. Cutting them in half, she has four magnets; cutting again, she has eight.
Using a magnifying lens, she kept cutting until the bits became invisible to the eye. Invisible, but still magnets. She could keep cutting until there are only atoms or only bare electrons. Still magnets.
Electrons are the tiniest magnets. If a lot of them spin the same way, the material is magnetic. Iron isn’t magnetic and that’s because some electrons spin this way, some spin that way, and so they cancel out.
Electrons canceling is like one person rowing forward while another rows backward. The boat stays put. If only one person rows or if two row one way and a third rows the other, then the boat moves.
The boat moves as long as there is an unpaired rower. That is, someone rowing one way not paired with someone rowing the other way. Electrons are like that. All it takes is one extra going one way.
A material that has unpaired electrons is magnetic; it can become a magnet. Iron, for instance. A material that has paired electrons is non-magnetic. Copper is an example.
A steel bolt isn’t magnetic. Steel is mostly iron, as much as 99% iron. But put the steel bolt near a magnet and patches of electrons called domains align in the same direction and the bolt becomes magnetic.
A magnet will stick to another magnet because opposites attract. A magnet will stick to a steel bolt because it magnetizes the bolt. A magnet won’t stick to a stick of wood because wood has no domains.
Another way to make a magnet is to run electric current through wire. The magnetic field is invisible, but a compass near a wire that is part of a circuit will be affected by the magnetic field through the wire.
An electromagnet is the basis for an electric motor. Lay a battery on its side and balance a disc magnet on the battery. Tape a paperclip to one end of the battery. Another to the other end of the battery.
Loops uncoated copper wire around and around into a coil of many loops, but leave the ends sticking out from the coil like –O– and insert the ends like arms into the paperclips. The coil will start spinning.
The sticking-out ends are a miniature drive shaft. This is the basic motor for everything from a toothbrush to a garage door opener. The battery creates electrical current and magnetic field in the wire.
The loop becomes an electromagnet. It is first attracted to and then repelled by the disc magnet on the battery. Attracted, repelled, Attracted, repelled. Around and around it spins, turning the drive shaft.
things wear down unless kept up
Messy Party, Magnetic Slime, and Crumbling Cookies
While making home-made gifts, Lacy discovered that things deteriorate. Batteries run down, unless recharged. Her room gets messier, unless cleaned up. That’s entropy for you: the tendency of things to become more disorganized, less useful.
LACY
Perhaps entropy is why the classroom becomes chaotic when the teacher leaves the room.
Entropy is at work at a party. At first, the chairs are all lined up. Gifts, neatly wrapped. Clothing pressed and food ready to serve. As the party wears on, there is more to clean-up, tidy-up tomorrow.
Lacy wants a gift for Alan, ideally one that does not become more disorganized. Perhaps a jig-saw puzzle. Out of the box, the pieces are jumbled up. Putting the picture together, there is less and less chaos.
That is, unless the bigger picture is taken into consideration. The food consumed by those putting it together. The gasoline used to shop for food. Electricity for lighting and energy to make the cardboard.
Life itself seems to wear down considering the resources needed going from a baby to senior citizen. So when thinking of entropy, Lacy needs to consider all that goes into making and playing the jig-saw puzzle.
Lacy decided to make magnetic slime. She mixed white glue (the kind used in school), water, green food colouring, baking soda, and iron filings. It mixes into a putty that does not appear organized or useful.
Magnetic slime sits there like a snotty blob—until near a magnet. The blob will ooze along to follow the magnet and, if close enough, snap out to catch the magnet like a frog catches a fly. Drop on a refrigerator magnet and the blog wraps around, swallowing up the magnet like a sci-fi creature. In the presence of the magnet, the blob seems to become more organized and capable of movement.
Cleaning up, it occurs to Lacy that the blob is like the jig-saw puzzle, given the effort and resources that go into it. That’s when she bumped her mug of cocoa and the mug shattered on the kitchen’s tile floor.
Lacy tried putting the pieces back together, like Humpty Dumpty. Forces between molecules hold a cup together, so putting pieces together carefully they should stick by attraction between molecules.
It doesn’t work. To adhere, surfaces must be unimaginably close, about the width of an atom. Solid surfaces are too rough to allow more than a tiny amount of their surface area to be this close.
The liquid glue used to make the magnetic blob worked better. Most adhesives are liquid, at least initially, because of the need for close contact between the glue and the materials being stuck together.
A liquid glue can flow into surface irregularities to provide the needed close contact. Close contact is also prevented by settling dust particles and distortion of the cup during the break.
Unfortunately, white glue does not form strong bonds and Lacy relegated the mug to the trash. She poured a glass of milk and took out a cookie. No hot cocoa, so cookie dunked in milk would do.
Dunking draws the liquid into pores in the cookie and dissolves the sugar structure of the cookie. The cookie falls apart. The longer the cookie is submerged, the weaker it becomes. Structures deteriorate.
resistance acts to oppose flow
Fresh Toast, a Babbling Brook, and Perpetual Motion
The family-history quiz Lacy made for her grandmother uses a simple circuit. Connecting a question with the correct answer, completes the circuit and a small bulb along the circuit lights up.
To light up, the bulb is incandescent. Inside the bulb is a thin wire coiled up to create resistance. If there is enough resistance, the wire will heat up and produce light. A little light; a lot of heat.
Water flows through a hose. If the hose is long and thin, that makes the flow more difficult. Electric current passes along a conducting wire. If the wire is long and thin, it too resists flow.
Incandescent bulbs are usually made with a long, thin coil of tungsten in a bulb of argon or nitrogen gas. Tungsten resists corrosion. Inert gas prevents the filament from burning out as it would in oxygen.
Incandescent lightbulbs give light. Mostly they give heat, about 95%. Heat from a light bulb is wasted and again shows that things deteriorate, becoming less useful.
Some appliances make use of resistance through a wire when heat is wanted more than light. A water hater, for instance, or hair dryer or a toaster. In such cases, it is not light but heat that is useful.
The wire in a toaster is made of nickel and chromium. It can become hot, but does not rust or melt. When hot, it gives off visible light and appears red, but toasts the bread by infra-red heat.
Toasting is not the same as burning bread, turning it to carbon like the ash from a fireplace. Toasting causes sugar and amino acids (which make protein) in the bread to change the texture and flavour.
The same process occurs when barbecuing, roasting, or baking. Going from raw meat to steak well-done. From uncooked potato to crisply roasted. From pie dough to a golden crust.
Resistance occurs in water circuits as well, similar to an electrical circuit. For water, the source is a pump. For electricity, a battery. They are connected by a pipe or wire; controlled by a valve or switch.
Lacy made her mom a miniature babbling brook for relaxing white noise at the end of a busy day. The waterfall sound is similar to the toaster’s heat in that both are the result of resistance along a circuit.
She bought a fish tank at the garage sale. A pump at the bottom of the half-filled tank draws water in from one side and pushes it up a tube, along a small diving board, and onto rocks and pool below.
The water flow encounters some resistance through the tube, but in the rocks as well. Were there no resistance and a perfectly smooth circuit of water, there would no babble to the brook.
The water falling into the tank turns a small fan. As the blades turn, they rotate a coil between magnets and produce an electrical current—basically, the same way electricity is generated at a hydroelectric dam.
Falling water or steam or even pedal power can be used to turn a coil between magnets and generate electricity. As Lacy pedals her bicycle, the tire turns a coil in a generator that powers the bicycle headlight.
The water pump generator helps power the pump, but it alone is not enough to power the pump since there is resistance and lost heat. If it could, it would be a perpetual motional machine and defy entropy.
measurement affects what is measured
Pumped Tires, Active Fans, and Uncertainty in Photography
Lacy’s bicycle, like most bikes, has pneumatic tires. They have to be pumped up. There is a recommended pressure imprinted on the side of the tire and she pumps the tire to the maximum and a little more. Over-filling makes the tire more rounded for less contact with the road. Less contact means less resistance due to friction, and her peddling becomes more efficient.
Although Lacy pumps each tire to the max, when she removes the pump head, air escapes. Sometimes a little and, when she has more difficulty disengaging the pump head, sometimes a lot.
As a result of escaping air, Lacy never knows exactly what pressure is in the tires. Even over pumping results in a best estimate, not accurate measurement. There is a certain amount of uncertainty.
Lacy is a cub reporter for the town newspaper and covers baseball. She conducts interviews and moves about the ballpark taking pictures, often catching the eye of local or visiting teams. Even a slight distraction can have an impact, such as a player distracted by the flash of a camera. At times Lacy affects the outcome in the process of reporting: news reporter turned newsmaker.
It is not possible to accurately observe or measure that which is modified by the process of observing or measuring. Reporting that changes what is observed is making news rather than reporting news.
The crowd can get into the game with enthusiastic cheering and chanting, inspiring the players. Even those watching the game televised feel their cheering can have an impact on the outcome. Except there is no feedback loop from those watching on television to the players. However enthusiastic the cheering at a local pub, viewers have no impact. They are passive.
It might make a difference if the players knew how many fans were watching the game televised. More viewers, more enthusiasm to perform which, in turn, might impact the outcome of the game.
Clay pitched a fast ball and Alan hit it out of the park. Lacy’s photo, with a slow shutter speed, showed a blurry image of the ball. It gave a sense of speed and direction, but not the ball’s exact location.
Ajay’s camera, with a fast shutter, shows the baseball in focus. Its exact location can be determined from the background, but the ball appears suspended, with no indication of speed or direction it was headed.
