# Is there a way to break down the Culomb?

1. Dec 21, 2008

### swraman

Most units in mechanics can be broken down into a combination of length, mass, and time.
eg. power = mass * distance * time^-2 * distance * time^-1 (force*velocity)

Is there any way to break the culomb down into mass, length, and time?

2. Dec 21, 2008

### mgb_phys

Yes from the definition of the Ampere
"One ampere is defined to be the constant current which will produce an attractive force of 2×10^–7 newton per metre of length between two straight, parallel conductors of infinite length and negligible circular cross section placed one metre apart in a vacuum"
And a coulomb is 1 Amp for 1 second.

Last edited: Dec 21, 2008
3. Dec 22, 2008

However, the ampere is its own SI base unit, independent of the kilogram, metre, and second. In the SI system, the coulomb cannot be written in terms of these three base units.

However, in other unit systems, such as cgs (of which there is more than one type), units of charge are defined in terms of the other base units (centimetre, gram, second), but that is only due to the way they are defined, rather than anything physical.

4. Dec 22, 2008

### cabraham

The Coulomb cannot be resolved into mass, length, and/or time quantities. Electrical phenomena require the addition of a 4th base quantity to define them. The base electrical unit is the Coulomb, and all other electric/magnetic quantities are defined from the coulomb.

But, it is difficult to establish a measurement reference based on the Coulomb at this present time. If we define the amp as the current which results in a specific force between 2 conductors, it is precise and repeatable. So we define the amp per the above post, and the Coulomb is 1 amp * 1 sec. The Coulomb is actually more basic than the Amp, but it is easier to establish the Amp as the reference. I hope this helps. BR.

Claude

5. Dec 23, 2008

### swraman

thanks

6. Dec 28, 2008

### rcgldr

A coulomb is then equal to exactly 6.241 509 629 152 65×1018 elementary charges. Combined with the present definition of the ampere, this proposed definition would make the kilogram a derived unit.

http://en.wikipedia.org/wiki/Coulomb