# Error in applying Coulomb's law

1. Nov 4, 2014

### mpatryluk

Well, it's not so much an error as it is a fundamental lack of understanding about multiplication of units greater than vs less than 1.

1. If two charges are repelling each other which have values greater than 1, then the value of q1q2 will be greater than the individual values charge values of each charge. However if the values are less than 1 coulomb, then instead of increasing, the value of q1q2 will decrease from that of the individual charges. How can this be?

2. If I q1 = 0.5 coulombs and q2 = 0.5 coulombs, then q1*q2 = 0.25 coulombs. But if I were to use millicoulombs instead, then 500 mc * 500 mc = 250,000 mc, which = 250C. Where is the error in my reasoning please?

Last edited: Nov 4, 2014
2. Nov 4, 2014

### Staff: Mentor

500 milliCoulombs times 500 milliCoulombs is 250,000 microCoulombs. The easiest way to see this is to write all the numbers out in scientific notation using the same units: $(500\times{10}^{-3})\times(500\times{10}^{-3})=(500\times{500})\times(10^{-3}\times{10}^{-3})=250000\times{10}^{-6}$.

3. Nov 4, 2014

### mpatryluk

Ahhh ok, everything has to be expressed in terms of scientific notation in relation to the coulomb being 10^1. I see, thank you.