Textbook Material to Read

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Chapter 18

18.1 Static Electricity and Charge: Conservation of Charge

18.2 Conductors and Insulators

18.3 Coulomb’s Law

18.4Electric Field: Concept of a Field Revisited

18.6 Electric Forces in Biology

Chapter 19

19.1 Electric Potential Energy: Potential Difference

19.2 Electric Potential in a Uniform Electric Field

19.3 Electrical Potential Due to a Point Charge

Main Concepts

Basic Charge

The magnitude of a basic charge is 1.60 x 10^-19 C (coulomb).

The Law of Conservation of Charges

The law of conservation of charge ensures that whenever a charge is created, an equal charge of the opposite sign is created at the same time.

Coulomb’s Law

This law calculates the magnitude of the electrostatic force $F$ between two point charges $q_1$ and $q_2$, separated by a distance $r$.

$F=k\frac{|q_1{q}_2|}{r^2}$

The constant $k$ is 8.988 x 10⁹ N m²/ C².

• The electrostatic force between two subatomic particles is far greater than the gravitational force between the same two particles.

Electric Potential

• Electric potential is potential energy per unit charge.

The electric potential $V$ of a point charge $Q$ is given by

$V=\frac{kQ}{r}$.

The constant $k$ is 8.988 x 10⁹ N m²/ C².

$r$ is distance from the point charge.

Electric potential is a scalar, and electric field is a vector.

Electric Field

Electric field $\mathbf{\text{F}}$ for a point charge $Q$ is given by

$E=\frac{kQ}{r^2}$

The constant $k$ is 8.988 x 10⁹ N m²/ C².

$r$ is distance from the point charge.

• The electrostatic force field surrounding a charged object extends out into space in all directions.

Conductors and insulators

• Any substance that has free electrons

and allows charge to move relatively freely through it is called a conductor.

• Other substances, such as glass, do not allow charges to move through them. These are called insulators.

Additional Resources

OpenStax High School Physics, chapter 18 Static Electricity

YouTube: video on the electric field around a charge