Section 4
Part 3
Understanding Electricity
Using Other Physical Systems
Dam example:
With a dam the power generator is called a turbine.
Water pressure ( created by gravity ) behind the dam moves water through tunnels to the bottom and opposite side of the dam. Inside the tunnels are blades that are connected to a shaft. The water pushes on the blades, spinning the shaft. Connected to the shaft are large magnets. The magnets move through several sets of coils. One set of coils generates current in one direction and another set of coils generates current in the opposite direction.
The current in the two coils are routed to a circuit that joins the two currents on opposite ends of another coil. This produces a very large current at a low voltage.
That end coil is the primary coil of a transformer. The other half of the transformer is another coil, that is wrapped differently than the first coil. The type of transformer used is a step-up transformer because it will convert the high current low voltage on the primary side to a low current high voltage on the secondary side. The transformer's output is connected to power lines which transfers the power to where ever it is needed ( your VCR ).
Microphone and speaker example:
A micro phone converts sound energy into electrical energy. A simple microphone is made of a sheet of paper suspended on a frame. Attached to the center and backside of the paper is a magnet. A coil is wrapped around the magnet. When you speak into the microphone the varying air pressure vibrates the paper which in turn vibrates the magnet inside the coil which causes electrons to move in the circuit attached to the coil ( inductor ).
A simple speaker works in the exact opposite way of a microphone. The varying electron flow in the circuit produces an electric field across the coil which cause the magnet to vibrate which cause the paper to vibrate which changes the air pressure around the paper which we hear as sound. Yes a microphone and speaker can be interchanged, but most audio equipment will not electrically or physically work efficiently that way.
In the AC circuits example, the signal source could be a microphone. In a real circuit, your voice would be used to change either the frequency ( FM ) or amplitude ( AM ) of the signal source, because to transmit sound with an electric or magnet field would require a vary large antenna.
The thunder cloud example:
Refer to figure - Thunder Cloud.
A water molecule is composed of two hydrogen atoms and an oxygen atom designated this way H2O.
Winds moving in a cloud will strip off a hydrogen nucleus from a water molecule. This creates two ions, H+ and HO-. The hydrogen ion being very light is pushed to the top of the cloud. The ionized water molecule being heavy is pushed to the bottom of the cloud. The top of the cloud becomes the anode ( positive plate ) and the bottom of the cloud becomes the cathode ( negative plate ). The air in the middle of the cloud becomes the insulator. The cloud is now a battery or the equivalent of a charged capacitor.
The negative ions on the bottom of the cloud causes the ground and air below to ionize ( repels the electrons ) causing them to become positively charged. The positive ions of the ground pull electrons out of the air, forming a positive ion path. The negative ions below the cloud repel electrons in the air and attract the positive ions, leaving behind a pool of electrons, forming a negatively charged path. The ionization occurs like cracks in a wall. The cracks appear as streams which can be seen when your hair stands on end. These ionized paths ( there are many ) grow from the bottom of the cloud ( negative charge ) to the ground and from the ground to the cloud ( positive charge ). Since the charge in the cloud is greater than the charge on the ground, the paths from the cloud to the ground grow faster than the paths from the ground to the cloud. The path that ionization takes depends on the strength of the air at any given point and usually results in an ionization path splitting, producing forks ( multiple paths ). Eventually one or more ionized paths from the cloud will connect with one of the ionized paths from the ground. The first fork to make a connection to the ground discharges ( electrons move to negated the positive ions ), followed by electrons in the next nearest upper fork on the path. This process continues all the way back up to the cloud. The large source of electrons from the ionized water molecules in the cloud now descend down the ionized paths so fast that the heat from air friction causes the air to expand rapidly creating a pressure wave. Our ears hear this as a loud crack, clap or bang. The heat generated by the friction causes the air to burn giving off light, which is called a lightning bolt. This is why the air smells burnt during/after a lightning storm.
Since light travels faster than sound, you can measure the distance a lightning storm is from you by measuring the time difference between the lightning bolt seen and the thunder heard. Sound at sea level travels about 1,087 feet per second. Light travels about 1,582,891,200,000 feet per second ( 1.5 trillion feet per second ). Since the difference in the velocities between sound and light is so great and the distance between you and the lightning bolt is so short, that for all practical purposes, the light reaches you in 0 seconds and that the sound pressure wave begins it's journey when you see the lightning bolt. When you see the lightning flash start counting the seconds. It takes sound at sea level to travel 1 mile in about 4.86 second. So if it takes 5 seconds from the time you see the flash to the time you hear the thunder, then the lightning is about 1 mile away.
Most lightning occurs inside the cloud ( sheet lightning ). Lightning also occurs between the top of a cloud and the upper atmosphere ( seen only from space ). When lightning does come down, the electrons can be moving so fast that they bounce when they hit the ground. Most lightning bolts that hit the ground travel down through the dirt to a metal pipe. Digging around where lightning has hit will reveal the charred remains of anything in it's path.
A basic rule in all of physics is that energy always travels in the direction of least resistance. Living things control results by intentionaly changing the forces involved and thus changing the path that energy follows. This is the main difference between organic ( life ) and inorganic things. Life will alter forces to satisfy it's needs. Non-life just follows the path of least resistance.
Electricity - Technical and Safety Information, Introduction, Light
Last updated: Mar 4, 2011