Aboutcleggsan Expertise All technical areas of Electronics Engineering.
Experience BSEE, MBA, Design, R&D, University Research.
Senior Life Member of IEEE. Life Fellow of AES.
Organizations IEEE, Consumer Electronics Society, Audio Engineering Society.
Broad teaching experience; work experience mostly in consumer electronics and conversion from analog to digital technologies. Pioneer in digital audio at all levels.
Question I believe this point to be true:
IN THEORY: if you took the -ve terminal of a cell and bueried it in the ground no current would flow as there is no completed circuit, but if you took both terminals of a cell and bueried them in the ground, current would flow... there needs to be a completed circuit.
Say for example I was walking down carpeted stairs and some electrons were "wiped" of one of my shoes, when I touch a metal door knob, i get a shock, where is the completed circuit? do the eletrons flow from the carpet through the door knob and to my finger? (ie if the door knob was floating in mid air, would i still get a shock?)
van de graaf generators with only one sphere use the earth as the second sphere. If the metal sphere becomes very positive and you touch it electrons flow from the earth to the sphere cancelling the charge on it, we were told never to operate a van de graaf without grounnding it, but i was told that it would operate exactly the same with no ground, the sphere would still become +ve and you would get a shock when you touched the ground even though there was no complete circuit?
(i think of it like this: you can't discharge a capacitor by grounding one plate, both plates need to be grounded)
Your help is much appreciated.
PS: Do you know what causes the effect of a charged gold leaf electroscope discharging when a lit match is placed next to the plate? (something to do with the ionisation of the match head?)
Answer ONE: Current flow, as from a circuit connected to a battery, is actual movement of current (in amperes) that flow from one terminal to the other through the external circuit. Hence, ohms law applies, where the EMF in volts is equal to the current in amperes times the resistance in ohms.
TWO: But what about when the EMF in volts is very high, but there is no circuit for the current to flow and there is little or no current available? It is just a special case of ohms law. The voltage is very high, the current is very low and the resistance in ohms is very high. We think of clothing and carpets and the like as insulators, but in reality they do have some resistance and it is very high.
THREE: Also,the charge in coulombs is an accumulation of energy or power in joules that can be held in some location for a time until it "leaks off" such as in a capacitor. Our bodies can act as a large capacitor as can also the door knob or other object. The charge can be transferred from one place to another, for example, as in the cases you mentioned.
FOUR: The various electrostatic generators are merely wiping off electrons from materials and holding them as a charge. After some time the build up of EMF gets high enough that a spark is generated, a miniature bolt of lightning, when the voltage gets high enough to jump through the ionized air - which has now become a sufficient conductor of the very small amount of current.
FIVE: There are two possible physical phenomenon that take place with a match near a plate. One is the heat generated can actually create a force on the plate. Secondly, the light beam has a force by virtue of the quantum packets of light that impinge on the plate, as well. You can look these things up in a high school or college level physics book and read all about them. Also, try www.howstuffworks.com which has lots of explanations for just about everything you can think of.
Good question; I have given you a very brief explanation; there is much more to say, but I will wait for your further questions if you have them.
