# How is electric charge measured?

1. Apr 29, 2012

### jd12345

How do we measure the amout of charge body has. Can you tell me some instruments and how do they work.
Well i know how ampere is defined so one coloumb will be the current that flows in one second - but how can wemeasure that?

2. Apr 30, 2012

### Drakkith

Staff Emeritus
3. Apr 30, 2012

### jd12345

Its good to test if charge is present as the leaves will repel but how do you measure the amount of charge?
Perhaps i dont understand -

4. Apr 30, 2012

### Staff: Mentor

More charge => more force between the leaves => larger distance between them

The basic idea is that you convert the measurement of the charge to a measurement of some other property - like the distance between the leaves, or a current somewhere, or an acceleration of particles or whatever.

5. Apr 30, 2012

### truesearch

one technique is to transfer the charge to a known capacitor then measure the voltage across the known capacitor. Then use Q = C x V to find Q.
An instrument designed to do this is called an electrometer.
If you want to measure the charge on a capacitor then a vibrating switch can be used to alternately charge the capacitor from a battery then discharge it through a milliammeter. If the frequency of switching is known then the chatge transferred at each switching can be calculated from the current read by the milliammeter.