Why is charge a derived quantity

  • Context: Undergrad 
  • Thread starter Thread starter mc2_phy
  • Start date Start date
  • Tags Tags
    Charge
Click For Summary

Discussion Overview

The discussion centers around the nature of electric charge as a derived quantity within the International System of Units (SI). Participants explore the definitions and relationships between charge and current, as well as the implications of these definitions for measurement and standardization.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • Some participants note that current was measured before charge, suggesting a historical context for the definitions.
  • One participant lists the seven base units in SI, emphasizing that electric charge is derived from the fundamental unit of current (ampere).
  • Another participant explains that charge is defined as coulombs, which are equivalent to ampere-seconds, highlighting the practical reasons for this derivation.
  • There is a correction regarding the expression of charge in terms of amperes per second versus ampere-seconds, with participants acknowledging and clarifying this point.

Areas of Agreement / Disagreement

Participants generally agree on the definitions and relationships between charge and current, but there are nuances in how these concepts are expressed and understood, indicating some level of contention or confusion.

Contextual Notes

There are unresolved aspects regarding the implications of measuring charge versus current and the practical challenges involved in establishing standards for these quantities.

Who May Find This Useful

This discussion may be of interest to those studying physics, particularly in the areas of electromagnetism and unit systems, as well as individuals exploring the historical development of measurement standards.

mc2_phy
Messages
12
Reaction score
0
Why is charge a derived quantity?
 
Physics news on Phys.org


convention. Current was measured before charge.
 


There are seven base units from which all other units are derived.


-meter (length)
-kilogram (mass)
-second (time)
-ampere (electric current)
-kelvin (temperature)
-candela (luminous intensity)
-mole (concentration of substance)
​

Electric charge is measured in Coulombs, or Amperes seconds.
 
Last edited:
In SI, current is a fundamental unit (ampere) and charge is a derived unit (coulomb = ampere · second) for practical reasons. It's easier to implement the standard for current precisely, by measuring the force between two current-carrying wires, than it would be to implement a standard for charge precisely, involving something like measuring the force between two charges, or counting electrons.
 


AbsoluteZer0 said:
Electric charge is measured in Coulombs, or Amperes per second.
Ampere seconds, not amperes per second.
 


AlephZero said:
Ampere seconds, not amperes per second.

My apologies.
Edited and corrected.
 
No prob. Thanks for that. Really cleared it up
 

Similar threads

Undergrad Confused about work done on charge
  • · Replies 8 ·
Replies
8
Views
2K
Undergrad Parallel plate capacitor, charge imbalance VS charge redistribution
  • · Replies 1 ·
Replies
1
Views
2K
Undergrad Charging a small metal ball from a charged hollow sphere
  • · Replies 4 ·
Replies
4
Views
2K
Undergrad Electric Field of Uniformly Charged Infinite Plane
  • · Replies 6 ·
Replies
6
Views
536
Undergrad Why charge density of moving dipole is dependent on time?
  • · Replies 3 ·
Replies
3
Views
2K
High School Why is the test charge always positive?
  • · Replies 3 ·
Replies
3
Views
3K
Undergrad Capacitor surface charge movement current, relativistic effects
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad Maxwell's equations and the momentum of charge
  • · Replies 12 ·
Replies
12
Views
3K
Undergrad Small question about constantly accelerating charges
  • · Replies 10 ·
Replies
10
Views
1K
Undergrad Conservation of charge in the Universe
  • · Replies 24 ·
Replies
24
Views
3K