Electric charge and field. Force and field strength

09/03/2026

The online electric charge and field simulations on this page will allow you to learn in a practical way how these concepts of physics act and how they relate to each other. Electric charge and electric field are fundamental concepts in physics that describe the interaction of charged particles and the electric forces that act between them. We will discover how the force between charges is generated and what is the electric field strength.

What is electric charge in physics

Electric charge in physics is an intrinsic property of subatomic particles, such as electrons and protons. Charges can be positive (protons) or negative (electrons).

Force between charges. Coulomb’s Law

The force between electric charges is a fundamental interaction in physics; it is described by Coulomb’s Law, which states that the magnitude of the electric force between two point charges is directly proportional to the product of their charges and inversely proportional to the square of the distance separating them. Equally charged particles repel each other, while oppositely charged particles attract each other. In the International System of Units the unit of electric charge is called the coulomb (or coulomb, symbol C). The value of the constant of proportionality in this law depends on the medium in which the charges are located, but in a vacuum the value of 8.99 x 10⁹ N-m²/C² is commonly used.

What is the electric field in physics

The electric field in physics is the region of space surrounding an electric charge where an electric force is exerted on other charges. The electric field is represented by field lines, which are imaginary lines that indicate the direction and strength of the electric field at each point.

Electric field strength

The electric field strength (also called electric field intensity in some texts) is measured in units of force per charge, therefore in the International System it is measured in newtons per coulomb (N/C). The calculation of the electric field at a given point is done by applying Coulomb’s law, which states that the field is proportional to the magnitude of the charge that generates it and decreases as the distance increases.

Applications of the electric field

The electric field has numerous applications in everyday life and technology. For example, it is used in touch screens, in the charging of electronic devices, in the acceleration of particles in particle accelerators and in the generation of energy through the interaction of electric and magnetic fields in electric generators.

Explore the exciting STEM world with our free, online, simulations and accompanying companion courses! With them you’ll be able to experience and learn hands-on. Take this opportunity to immerse yourself in virtual experiences while advancing your education – awaken your scientific curiosity and discover all that the STEM world has to offer!

Electric charge and field simulations

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1791

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1879

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1775

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Test your knowledge

What physical principles define electric charge as a fundamental property of matter, and how does this property manifest in particle interactions?

Electric charge is an intrinsic property of particles such as electrons and protons, and it determines how they interact through electric forces. These forces can be attractive or repulsive depending on the type of charge: like charges repel, while opposite charges attract. Coulomb’s law describes the strength of this interaction, showing that the force depends on the magnitude of the charges and the distance between them. Electric charge is conserved—it cannot be created or destroyed, only transferred—which explains everyday phenomena like static electricity or the operation of electronic devices. Because charge is quantized and conserved, it plays a central role in the structure of atoms, the behavior of materials, and the functioning of electrical systems.

How does the concept of an electric field help describe the forces acting on a charge placed in space?

An electric field is a conceptual tool that represents how a charge influences the space around it. Every charge generates a field that assigns a specific force per unit charge to every point in space. The direction and magnitude of this field depend on the size of the source charge and the distance from it. When another charge is placed within this field, it experiences a force determined by the field’s characteristics at that point. This framework simplifies the analysis of systems with multiple charges, since fields can be superimposed. Electric field lines provide a visual representation of the field’s structure, showing how forces would act on a positive test charge.

Why can two objects attract or repel each other without touching? Where does that force even come from?

The force comes from the electric field surrounding any charged object. This field extends through space like an invisible influence. When another charged object enters that region, it feels a push or pull depending on the sign of its charge. No physical contact is needed because the interaction happens through the field itself—similar to how gravity pulls objects without touching them. It’s action at a distance, but fully explained by physics.

What happens if I bring two identical charges closer and closer together? Is there a limit to how strongly they repel?

If the charges are the same, the repulsion increases dramatically as the distance decreases. Coulomb’s law shows that the force grows as the inverse square of the distance, so the closer they get, the stronger the push. In theory, there’s no upper limit: the force keeps increasing. In practice, before reaching extremely tiny distances, other physical effects appear, but for everyday situations, the repulsion simply becomes stronger and stronger.

How is it possible that an object can be “charged” when it doesn’t look like anything has been added to it? Where is that charge actually stored?

The charge isn’t something visible or stuck on the surface—it’s in the electrons. When an object gains extra electrons, it becomes negatively charged; when it loses some, it becomes positively charged. The object doesn’t change shape or color, but its electrical behavior changes. That’s why a balloon rubbed on your hair can stick to a wall: it has gained electrons, and those charges interact with the charges in the environment. The charge is distributed across the object’s surface, even though we can’t see it.