Browse Definitions :
Definition

coulomb (C)

What is a coulomb (C)?

A coulomb (C) is the standard unit of electric charge in the International System of Units (SI). It is the amount of electricity that a 1-ampere (A) current carries in one second (s). A quantity of 1 C is equal to the electrical charge of approximately 6.24 x 1018 electrons or protons. This comes to about 6.24 quintillion particles.

In the SI standard, the coulomb is considered a derived unit, which means it is constructed from one or more of the seven base units, in this case, ampere and second. Prior to 2018, the base units provided the foundation for the SI standard, and the derived units were constructed from these. Now, the standard is built upon seven defining constants, and all base and derived units can be constructed directly from those constants. However, the SI standard has retained the concept of base and derived units because they are so well established.

One of the seven foundational constants is the elementary charge, which is the electric charge carried by a single electron or proton. The elementary charge (e) is 1.602176634 ⋅ 10-19 C. Both electrons and protons carry the same amount of charge. However, a proton carries a positive charge, and an electron carries a negative charge. So, the elementary charge can be positive (+e) or negative (-e).

By fixing the elementary charge at 1.602176634 ⋅ 10-19 C, the standard fixes the coulomb at a specific number of electrons or protons that make up 1 C of charge. The following formula can be used to calculate that number:

Q = n ⋅ e

The symbol Q represents the amount of charge in coulombs, and the symbol n refers to the number of electrons or protons. If both sides of the equation are divided by e, the number of particles in a coulomb can be calculated as the following:

Q = n ⋅ e

Q / e = (n ⋅ e) / e

n = Q / e (after reversing Q / e = n)

n = 1 C / (1.602176634 ⋅ 10-19 C)

n = 6.24150907 ⋅ 1018 C

In the fourth line, 1 C replaces Q because the objective is to find the number of particles in a single coulomb, and the elementary charge constant replaces the e. Based on this calculation, 1 C contains the charge of approximately 6.24 ⋅ 1018 particles, a number that would look something like this:

6,241,509,070,000,000,000

In terms of SI base units, 1 C is the equivalent of 1 ampere-second, which can be expressed as 1 C = 1 A ⋅ 1 s (or C = A ⋅ s). This can also be thought of as an ampere being equal to 1 coulomb divided by 1 s, as in 1 A = 1 C / 1 s (or A = C / s). In other words, if a current in a circuit is 1 A, 1 C of charge passes through a point in the circuit every second.

The basics of an electrical circuit
Diagram illustrating the basics of an electrical circuit

How does an ampere compare to a coulomb?

The ampere is the SI standard of electric current. This is in contrast to the coulomb, which is the SI standard of electric charge. One ampere is equal to the electric current that corresponds to the flow of 1 / (1.602176634 ⋅ 10-19) elementary charges per second. Before the SI was updated in 2018, the ampere was based on the force between two current-carrying conductors with a fixed value of vacuum magnetic permeability at 4π ⋅ 10−7 henries per meter.

The force with which two electrically charged bodies attract or repel one another depends on the product of their charges in coulombs, as well as on the distance between them. If the polarities are the same -- negative/negative or positive/positive -- the coulomb force is repulsive; if the polarities are opposite -- negative/positive or positive/negative -- the force is attractive. For any two charged bodies, the coulomb force decreases in proportion to the square of the distance between their charge centers.

See also: resistance, Ohm's law, reactance, admittance, susceptance and henry.

This was last updated in November 2022

Continue Reading About coulomb (C)

Networking
  • remote infrastructure management

    Remote infrastructure management, or RIM, is a comprehensive approach to handling and overseeing an organization's IT ...

  • port address translation (PAT)

    Port address translation (PAT) is a type of network address translation (NAT) that maps a network's private internal IPv4 ...

  • network fabric

    'Network fabric' is a general term used to describe underlying data network infrastructure as a whole.

Security
  • governance, risk and compliance (GRC)

    Governance, risk and compliance (GRC) refers to an organization's strategy for handling the interdependencies among the following...

  • total risk

    Total risk is an assessment that identifies all the risk factors associated with pursuing a specific course of action.

  • steganography

    Steganography is the technique of hiding data within an ordinary, nonsecret file or message to avoid detection; the hidden data ...

CIO
  • microtargeting

    Microtargeting (also called micro-niche targeting) is a marketing strategy that uses consumer data and demographics to identify ...

  • business process

    A business process is an activity or set of activities that accomplish a specific organizational goal. Business processes should ...

  • business process improvement (BPI)

    Business process improvement (BPI) is a practice in which enterprise leaders analyze their business processes to identify areas ...

HRSoftware
  • employee onboarding and offboarding

    Employee onboarding involves all the steps needed to get a new employee successfully deployed and productive, while offboarding ...

  • skill-based learning

    Skill-based learning develops students through hands-on practice and real-world application.

  • gamification

    Gamification is a strategy that integrates entertaining and immersive gaming elements into nongame contexts to enhance engagement...

Customer Experience
  • Microsoft Dynamics 365

    Dynamics 365 is a cloud-based portfolio of business applications from Microsoft that are designed to help organizations improve ...

  • Salesforce Commerce Cloud

    Salesforce Commerce Cloud is a cloud-based suite of products that enable e-commerce businesses to set up e-commerce sites, drive ...

  • Salesforce DX

    Salesforce DX, or SFDX, is a set of software development tools that lets developers build, test and ship many kinds of ...

Close