# Elementary charges

#### Fusilli_Jerry89

1. Homework Statement
1) How many electrons make up a charhe of 1 mu C?

2)What is the magnitude of the force a 10-mu C charge exerts on a 3.0-mC charge 2.0 m away? (1 muC=10^+/-6C , 1 mc=10^+/-3C)

2. Homework Equations
FE=(kQQ)/d^2

3. The Attempt at a Solution
1) (10E-6 C)/(1.6E-19)
I got 6.2E13 but the book says a micro columb is 1.0E-6, and the other book I have says it's 10E-6. Which is it?

2)FE=[(9.0E9)(1E-4)(0.03)]/4
=6750 N
The book says the 10-mu C charge is 10E-6 and the 3.0-mC charge is 3.0E-3.

I'm confused.

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#### berkeman

Mentor
I think it's just a limitation of the notation for exponential notation when not using LaTex or some other math typesetting tool.

A microColoumb is definitely $$1*10^{-6} C$$

And when you try to write exponential notation without using math typesetting, you can try to write it either of the ways you listed.

#### Saketh

2)FE=[(9.0E9)(1E-4)(0.03)]/4
=6750 N
That's not right.
2)FE=[(9.0E9)(10E-6)(3E-3)]/4
=6750 N
Once you figure out how to make the microcoulomb/millicoulomb conversion, you won't make the same mistake again. Don't mix up microcoulombs (E-6) and millicoulombs (E-3)!

$$10 \mu\rmmath{C} = 10 \times 10^{-6} C$$
$$3 \rmmath{mC} = 3 \times 10^{-3} C$$

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#### blastyournos

well if you use scientific notation its gotta be 1.0E-6, cant have anything more than 9 as the base.