How is electric charge measured?

Click For Summary

Discussion Overview

The discussion revolves around the measurement of electric charge, exploring various instruments and methods used for quantifying charge in different contexts. Participants inquire about the principles behind these measurements and the functionality of specific devices.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant asks about the instruments used to measure electric charge and expresses a foundational understanding of the definition of a coulomb in relation to current.
  • Another participant suggests an electrometer as a potential instrument for measuring charge.
  • A participant questions how to quantify the amount of charge, noting that while an electrometer can indicate the presence of charge, it does not directly measure the quantity.
  • It is proposed that the force between the leaves of an electrometer can indicate the amount of charge, with larger distances correlating to greater charge.
  • One method discussed involves transferring charge to a known capacitor and measuring the voltage across it, using the relationship Q = C x V to determine the charge.
  • A technique involving a vibrating switch is mentioned, where a capacitor is charged from a battery and then discharged through a milliammeter, allowing for calculation of the charge based on the current and known switching frequency.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding the measurement of charge, with some methods proposed but no consensus on a singular approach or instrument being definitive.

Contextual Notes

Some assumptions about the principles of charge measurement and the operation of instruments like electrometers and capacitors are not fully explored, leaving room for further clarification.

Who May Find This Useful

Individuals interested in electrical engineering, physics, or those seeking to understand the practical aspects of measuring electric charge may find this discussion relevant.

jd12345
Messages
251
Reaction score
2
How do we measure the amount 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?
 
Physics news on Phys.org
Its good to test if charge is present as the leaves will repel but how do you measure the amount of charge?
Perhaps i don't understand -
 
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.
 
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.
 

Similar threads

  • · Replies 3 ·
Replies
3
Views
1K
  • · Replies 20 ·
Replies
20
Views
3K
  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 58 ·
2
Replies
58
Views
6K
  • · Replies 16 ·
Replies
16
Views
2K
  • · Replies 29 ·
Replies
29
Views
3K
  • · Replies 73 ·
3
Replies
73
Views
6K
  • · Replies 24 ·
Replies
24
Views
2K
  • · Replies 3 ·
Replies
3
Views
1K