# Basic charge and coulombs

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1. Jun 28, 2015

### snowjoe

why isn't the number of e or p making a Coulomb the same as the reciprocal of the 'basic' charge if the basic charge is defined as a fraction of a Coulomb?

basic charge = 1.6 x e-19C, but number of p or e constituting a C is 6.25 x e18

Last edited by a moderator: Jun 28, 2015
2. Jun 28, 2015

### Orodruin

Staff Emeritus
Yes? 1/1.6e-19 = 6.25e18

3. Jun 28, 2015

### snowjoe

thank you. i may be getting stupid, but why isn't the number of e or p 1.6 e19, if each e or p, basic charge, has a charge

there's something i'm not getting. if a quantity x was 1/10th of y, it would take 10 x's to make y. why not 1.6 e19 e or p to make 1 C?

4. Jun 28, 2015

### Orodruin

Staff Emeritus
Because 1/1.6 is not equal to 1.6. Imagine instead that 1 C was the charge of 20 = 2e1 protons. This would make the basic charge 1/20 = 0.05 = 5e-2 C. Obviously, this is not equal to 2e-1, which it would be if you applied the same logic as the one you just applied.

Because 10*1/10 = 1 while 1.6e19 * 1.6e-19 = 1.6^2, which is not equal to one.

5. Jun 28, 2015

### Drakkith

Staff Emeritus
If quantity X is 0.2 of Y, then 1/0.2 = 5, meaning it takes 5X to equal Y. If X is 15 millionths of Y, then 1/0.000015 = 66,666, so it takes 66,666 X to equal Y.

6. Jun 28, 2015

### snowjoe

still, .2 is 1/5. and 5x = y so if a quantity is 1/ 15 millionth of another it would take 15 million of that quantity to equal that other, as it requires 5 of the amount that is 1/5 (.2) of another to equal that other amount

7. Jun 28, 2015

### Drakkith

Staff Emeritus
No it doesn't. I just showed you the math in my post.

8. Jun 28, 2015

### snowjoe

i know, the math makes sense, but i can't see my way around the logical demand that a fractional part of a quantity is that fraction because it takes the amount denominated to equal the whole quantity. the example of .2 follows this logic, five .2s equal the whole, .2 is the fraction 1/5

9. Jun 28, 2015

### SteamKing

Staff Emeritus
I have no idea what you mean here.

That's because 0.2 = (2/10) = (1/5) in its simplest terms, and 5 * (1/5) = 1.

However,
1 / 1.6 = 1 / (16 / 10) = (10 / 16) = 5 / 8 = 0.625

10. Jun 28, 2015

### Drakkith

Staff Emeritus
Yes, but look at your original numbers.
basic charge (c)= 1.6 x 10-19C
C = 6.25 x 1018c

1.6 x 10-19 is already a fraction equal to 1/6.25x1018, just like 0.2 is a fraction equal to 1/5. You multiply 0.2 times 5 to get 1, and you multiply 1.6x10-19 by 6.25x1018 to get 1.

If you're getting confused over the fact that 1.6x10-19 is not 1/1.6x1019, then the only way I know of understanding this is to just do the math.
1.6x10-19 = 1/X
1.6x10-19X = 1
X = 1/1.6x10-19
X = 6.25 x 1018

Similarly: 0.2 = 1/X
0.2X = 1
X = 1/0.2
X = 5

11. Jun 29, 2015

### andrevdh

Let's say it takes N electrons to make up one coulomb of charge then

N x e = 1 C

so

N = 1 coulomb / 1.6 x 10-19 coulomb

Historycally the coulomb, a certain amount of charge or electrons, was defined
via the ampere - the amount of current in 2 parallel wires 1 meter apart in a vacuum
when the magnetic force on one meter of these wires is 2 x 10-7 newton.

Last edited: Jun 29, 2015
12. Jun 29, 2015

### A.T.

Is math not logical enough?

13. Jun 29, 2015

### Orodruin

Staff Emeritus
I do not think this is where the OP's confusion lies, but rather in the fact that the reciprocal of 1.6e-19 is not 1.6e19, see post #4.

14. Jun 29, 2015

### andrevdh

Yes, that is why I started to mention the definition of the ampere.
Maybe that might clear it up.

15. Jun 29, 2015

### snowjoe

Thanks, you explained this beautifully

16. Jul 5, 2015

### snowjoe

yeh, math, logical, mind, not so much, sometimes

17. Jul 7, 2015

### andrevdh

The mind is much like a muscle.
The more you use it the stronger it gets.

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