Coulomb's Law Question

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EEC

Senior Member
Location
Maryland
Can you give an example of coulomb's law having a force of 120 volts and a distance of 500 feet? How would you find the the two charges?
 

BJ Conner

Senior Member
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97006
Count the electrons

Count the electrons

Count the electrons drifting by in the wire. Divide the number by 6.023 x 10^ 23 and thats how many amperes in the circuit.
 

EEC

Senior Member
Location
Maryland
Tons of force

Tons of force

Now I am reading that the force in coulomb's law in measured in tons not voltage. Is this correct?
 

EEC

Senior Member
Location
Maryland
Charges and Potenial difference confusing

Charges and Potenial difference confusing

This has been confusing me. We have negative (charges) electrons flowing because there is a difference of potenial in the Dc power source. The charges flow to the positive side of the DC source. They then flow from the positve side in the DC source to the negative side in the DC source. The negative side of the DC source continues to have a excess of negative (charges) electrons. I would think that positive charges would be needed to attach the negative charges. I don't know what to call the positive charges?
 

charlie b

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Staff member
Location
Seattle, WA
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Electrical Engineer
I don't know what to call the positive charges?
Some have used the phrase, "holes in the atoms where electrons are supposed to reside," or simply "holes." If an atom that is "missing and electron" (i.e., is a positively charged "hole") obtains an electron from its neighbor to the left, you can say that a negative charge moved to the right, or that a positive "hole" moved to the left. They are functionally identical. By convention, current is described in terms of the motion of positive charges, despite the fact (perhaps not known when the convention was first adopted) that it is a negatively charged particle that is actually in motion.

 

charlie b

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Staff member
Location
Seattle, WA
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Electrical Engineer
6.24151?10e18 electrons (or protons). Not the same as Avagodro.
Correct (almost). The motion of protons is seldom the physical basis for current flow. But as to Avogado, his number of 6.023 E23 would be the number of electrons that you would have, if you had a "mole" of electrons. ;)

 

mikeames

Senior Member
Location
Germantown MD
Occupation
Teacher - Master Electrician - 2017 NEC
6.24151?10e18 electrons (or protons). Not the same as Avagodro.
I was going to mention this but then I figured....... Someone will think I googled it. I memorized it a while back along with many others formulas capacitive (1 over 2 pi fc squared) and inductive reactance ( 2 pi fl) simply to learn it. I may be wrong on those formulas but I use to know it. Not something your average EC needs to know on a daily basis.

I guess Larry is a good judge of character.
 
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Finite10

Senior Member
Location
Great NW
My brain hurts

My brain hurts

Acceleration of gravity is 9.8 m/s^2
After that I'm looking stuff up. Life is open book.

This stuff is hard to talk about. Permittivity changes in free space versus air, which makes 'k' a bit higher. Kinda like when something is off the earth's surface and mass is less affected by gravity's acceleration, so weight is less.


Also, all the super script and subscript stuff is a pain online. And forget Greek letters here. Who is the cruel task master asking you to solve a Coulomb's problem, a physics class?

k = 9.0 x 10^9 Nm^2/C^2
k is a constant, C is a charge (sometimes expressed as Q)
K can also be;
k = 1/(4 x 3.141 x epsilon-o)
where epsilon-o = 8.85 x 10^-12C^2/(Nm^2)

Now use the constant 'k';
Electric Force = F = k(q1q2/r^2)
Where q1 is a +ion, and q2 is a -ion, and r the distance between them.

I don't know about no avocado numbers or oily numbers, they don't have any value to me - presently.
 
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