Is this the only reason?
What about the direction of current flow?

What does it matter?
In your body, the charge carrier is both positive and negative, positive ions and negative ions.
Current flows in both directions.

 

Is this the only reason?
What about the direction of current flow?

When your body is acting as a conductor and you are getting an electrical shock give which direction the current is flowing some thought and consideration and then get back to us with if it matters.

Shocking! Positively shocking! Now do we thing the guy in the tub figured the direction of current flow mattered? You were given links and explanations. There is not much more you need to know.

Ron

 

The concept of current is the measure of charge movement RATE. Again....current is defined as a RATE. It can have any polarity or any one direction.

It is one coulomb of charge per second is the standard RATE unit. So if the RATE of flow movement is one coulomb per second we call it one amp. I hear they are going to re-define this.

One volt used to be call the strength of an electric field, of one coulomb, one meter away. I don't know what they call it now. It also could be any polarity and direction.

Anyhow...in an electric/electronic circuit, the only charge carrier that moves and can flow.....is the negative electron. However........this physical flow can be mathematically inverted and called positive flow. The fundamental reason we can do this.......is because the positive charge in a circuit....CAN NOT move. But I don't think you were asking bout that.

In a bag of ionic solution, or electrolytic solution......Both positive and negative charges CAN move.

Any charge movement can be called current now. An atom or molecule with a net charge, and moves, can be called current.

So...if you think about it.....any current that comes into the body.........causes TWO current flows....inside the body.

 

DC polarity sometimes does matter (because of the physical movement of charged matter) if you are generating controlled arcs as any welder knows because of the material difference in anode cathode heating characteristics due to rod coating, gas flows and plate sizes/shapes.

Direct current electrode positive (DCEP) is what we used to call reverse polarity. Direct current electrode negative (DCEN) is what we used to call straight polarity. I suspect the same person who changed the word library to thelearning resource center got a hold of these terms.

In DCEP the electricity flows into the tip of the welding rod and concentrates about two-thirds of the heat, which gives good penetration. DCEP is usually used on thicker steels.

In DCEN the electricity flows out of the rod, concentrating about one-third of the heat on the rod. Less penetration makes this a very good choice for thinner steels.

http://www.esabna.com/euweb/awtc/lesson2_6.htm

It's a bit of common physics that's used every day.
http://nptel.ac.in/courses/112107090/module2/lecture1/lecture1.pdf

 

I have a problem yet.
As it is clear in this video, the spark direction is from center electrode (positive) to the body of the spark plug (negative).

How is it possible?
I'm curious about this matter.
Thanks.

 

I have a problem yet.
As it is clear in this video, the spark direction is from center electrode (positive) to the body of the spark plug (negative).

How is it possible?
I'm curious about this matter.
Thanks.

Stop being obsessed with the direction of the spark.
You cannot see electrons. What you are seeing is the ignition of gas molecules caused by the ionization of the gas molecules. Which end ignites first has to do with the breakdown potential of the gas, not the polarity of the charge carrier.

 

The spark I see in the video is the output of an ignition transformer. How do you figure a positive and negative with the output of a high voltage induction transformer, for example an ignition transformer? Maybe you should read some inductive theory and transformer theory? You are taking this way too far.

Ron

 

.......Also it seems the spark direction is from the centre electrod to the body of spark plug. (From positive to negative)

Why do you assume the center electrode is positive?
It could be either, depending upon the direction of the coil secondary winding.
In lost-spark designs where one coil is connected to two plugs in series with their bodies as common, one has a positive polarity center electrode and the other has a negative.

 

If you go back to post #7 and watch the video the helicopter is not grounded and yet when the rod connected to the helicopter it draws an arc. Why? When I walk across a wool rug in the winter and reach for a door knob which is not grounded I draw an arc, why? More specific what does the rod extended from an ungrounded helicopter draw that arc? Got any ideas?

Ron

It's not the voltage of the wires that is the concern -- it's the static charge on the helicopter. Stand on the ground and grab a cable dangling from a hovering helicopter and, on most days (humidity has a huge impact, just as it always does with static electricity), you are going to get knocked on your butt (and possibly a nice funeral shortly thereafter). The arc is the result of equalizing the static charge on the helicopter to whatever it is coming into contact with so as to put them at the same potential. Because there are several mechanisms that result in the net charge on a helicopter, the charge can be either positive or negative. The average charging current is typically very small -- in the microamp range -- but the voltages can easily build up to several dozen kilovolts relative to the surroundings.

 

It's not the voltage of the wires that is the concern -- it's the static charge on the helicopter. Stand on the ground and grab a cable dangling from a hovering helicopter and, on most days (humidity has a huge impact, just as it always does with static electricity), you are going to get knocked on your butt (and possibly a nice funeral shortly thereafter). The arc is the result of equalizing the static charge on the helicopter to whatever it is coming into contact with so as to put them at the same potential. Because there are several mechanisms that result in the net charge on a helicopter, the charge can be either positive or negative. The average charging current is typically very small -- in the microamp range -- but the voltages can easily build up to several dozen kilovolts relative to the surroundings.

I understand that. I was trying to pry that information out of the original poster who apparently ignored my post and many of the questions aimed at getting them to do a little research and learn. Matter of fact, using your example of a landing helicopter wasn't that one of several theories as to what went wrong with the Hindenburg Landing? Anyway I was trying to get the same potential out of the original poster but thanks.

However my one portion should have read:
More specific what (should read why) does the rod extended from an ungrounded helicopter draw that arc? Got any ideas? Anyway it apparently fell on deaf ears with the exception of you.

Ron

 

Thank you all.
But if you touch or even put your hand near the spark plug wire that's disconnected from the plug, you maybe experience the electrical shock although the automotive has been isolated form ground via rubber wheels.
Also it seems the spark direction is from the centre electrod to the body of spark plug. (From positive to negative)

You are confusing different meanings of "ground". The "ground" of a car is almost always the frame and the frame is usually (not always) connected to the negative terminal of the battery. This has absolutely nothing to do with the "ground" that you walk on. The proper name that should be used for the electrical potential of the car frame is "common", but that is uncommonly used.

The ignition system results in a large voltage (several dozen kilovolts, typically) relative to the car frame. If the spark plug is disconnected, it can be much more than that because the inductive kick of the coil will produce whatever voltage is needed in order to get the current to flow. If the easiest path for that current is through you, to the physical ground, up through the tires, and on to the frame, then that's the path that most of the current will go.

 

Electron flow is from negative to positive in a circuit.
Electron flow is from positive to negative inside a battery feeding the circuit.

The conventional current flow is ficticious, arbitrarily defined from positive to negative inside a circuit, and that is a convention, not a fact. Current is the flow of electrical charge carriers.

You are quite incorrect on that last point -- current is the flow of CHARGE, not of charge carriers. It is measured in amperes which, by universally agreed upon definition, is coulombs/second and coulombs is a measure of charge that is a signed quantity. The assignment of what is positive charge versus negative charge is arbitrary, but is also quite universally agreed to. Electrons are negatively charged. Period.

Thus if you have ~6.2E18 electrons flow from Point A to Point B, the amount of charge that flowed from Point A to Point B is -1 coulomb. If this happened over the course of one second, the current that flowed from Point A to Point B is -1 ampere. If you want to use the direction of the charge carriers (the electrons) as your reference direction for current, that's fine. But then the current that flowed in that direction is negative.

 

Doesn't mater except in particle accelerators (like cathode ray tubes).

It really doesn't even matter there. It is easier for humans to visualize the mechanisms by thinking of the flow of charge carriers, but everything still works out just fine whether you properly use electron flow or conventional current. And of course the physics of the device determines what direction of current is possible, but that is independent of what we call things.

One area where it really matters are Hall effect devices. Here you have moving charge carriers interacting with a magnetic field. As a consequence, positive charge moving one direction is NOT the same as negative charge moving the other in this case. This is one way to experimentally show the sign of the charge carriers in a device.

 

Ben Frankin made a mistake. Period. We didn't change what was accepted for a long time because 99% of the time it doesn't matter.

When it does matter we might invent concepts of "holes" and "electrons".

It matters in solid state physics, electron beam deflection and chemistry. All subjects I worked or was trained in.

"electrons" don't "flow" either, but the water analogy in a pipe works for a while. It's probably more like bumping cars.

Somewhere along the line, I learned that electrons are in circular orbits. Later, when you can understand probability I learned of predictability of being a in a particular space. Nobody told me later, I would learn differently. So, we kinda learn at the level we can understand or like telling children concepts; e.g. death or sex to a 3 YO, a 10 YO and an 18 YO. It's not wrong.

I once took a class and I challenged teach about the answer to a question. I won with the teach's explanation of "Your not supposed to know that yet".

There are lots of phenomenas that you don't usually need to know. I did.

A wire moved in free space generates current. It's a wire in the Earth's magnetic field. Physics says it generates a current and it does. It's really tiny one. If your measuring 1e-12 Amps in an environmental chamber with a fan, the wires move unless taped down.

Flexing a coax cable generates charge. It's the triboelectric effect. Graphite is used to lessen this effect.

In some cases three 1K resistors in series does not equal 3K because of parasitics.

In other cases SMT resistors mounted on their side has a lower parasitic than mounted the wide side down.

"Ideal" circuit elements don't exist. You have to account for this at times.

 

Ben Frankin made a mistake. Period.

Ben made an arbitrary choice with a 50% chance of being right, since the necessary instrumentation to determine the charge polarity of an electron would not be available for another century or so. Now, of course, anyone can do it with a vacuum tube (valve).
If he had happend to make the other choice he would have looked like even more of a genius than he was.

 

As an added note, Edison could have used the "Edison Effect" noticed in 1883 in an experiment with the incandescent lamp to realize that the charge of the carriers had to be negative, but I don't think he did.