kyweathergal said:
I have heard that once lightning reaches the ground, it depends on soil content as to how it disperses. i.e. sand for instance, disperses it rather quickly. Clay soil takes longer to disperse this energy. I have often wondered what happens with all that energy. Where does it go?
With lightning, the direction of em energy flow is inwards towards the plasma channel. Before the lightning strike, the energy is stored in strong e-fields between clouds and earth. During the strike, the em energy flows from the e-fields towards the lightning.
Note that the energy doesn't flow along the channel. A lightning channel contains a flow of electricity (charge,) not a flow of energy. Most early textbooks will conflate charge and energy, confusing everyone. Is a flow of electricity called Electric Current? But that 'electricity' cannot be a form of energy, since coulombs aren't joules. "Electricity" becomes impossible to understand unless you can find some animations of the amperes of charge-flow depicted as distinct from the watts of em energy-flow.
During lightning, the charges flow along the channel, while the em (electrical) energy flows inwards towards the channel from the surrounding space. And, after the lightning strike is over, the fields between cloud and ground are weaker, and a hot column of air is left behind. Energy wasn't injected into the ground. It was injected into the miles of lightning channel, creating a hot air column and lots of light and radio waves. To "harness lightning" we'd have to replace a portion of that channel with some sort of man-made device, then create an impedance match between the device and the lightning. That maximizes the rate of energy transfer into the device. During operation, our device would produce an enormous back-EMF which was enough to actually reduce the amperes in the main lightning discharge.
High-volt capacitor discharge is similar to lightning: imagine a spark leaping through the dielectric between the two capacitor plates. The em energy starts out as e-fields stored in the dielectric between the plates. During the spark, the em field-energy between the two plates flows towards the spark. At the same time a large current appears inside the narrow spark. But electric current is not a flow of energy. The energy-flow and the charge-flow have two entirely different pathways.
Heh, the big long-running debate about "the true direction of electric current" is irrelevant in showing us the direction of energy-flow during a spark. The em energy flow resembles a contracting cylinder of onion-layers, with the spark being at the center of this cylinder.
The problem of harnessing lightning is similar to the problem of harnessing the energy in a current-carrying loop of superconductor wire. If the voltage drop along that wire is zero, then we can't extract any em energy. And, without a voltage drop there really is no em energy flowing along the wire in either direction. The energy just sits there in the surrounding magnetic field. To pull out some energy, insert a resistor which produces a voltage-drop, a back-emf, and which causes the value of current to be reduced. Then the em energy will flow into the resistor from both directions along the wire. Essentially the magnetic fields collapse inwards toward the resistor. Analogy: if you rub your thumb against a spinning wheel, the Kinetic Energy of the wheel flows into your thumb, creating frictional heating. End result: halted wheel, hot thumb. Which way did the energy flow? It didn't spin with the wheel. Instead it flowed across the wheel, approaching your thumb from all directions.
