Electrostatics

Introduction

Have you ever walked across carpet in the winter and then received a small shock when you touch something metal like a door handle? Have your clothes ever stuck together when you take them out of the dryer? Have you ever had your hair stand on end when you take off a sweater or sweatshirt? These are all simple phenomena related to the build up of charged particles. While mankind has known about the effects of electrically charged particles for thousands of years, it was only in the past hundred years that we were able to identify the source of electrical charges and model their behavior. In this unit you will take a deeper look into charges beyond the 'likes repel and opposites attract' teachings of elementary school. We'll learn to calculate those attractive and repulsive forces and to show how invisible fields are responsible for them. We'll also look at how that charge can be stored in devices, called capacitors, for later use.

Essential Questions

Why do objects have an electric charge?
How do objects become electrically charged?
How do we model the interactions between charged objects?
What causes electric fields?
What is electric potential?
What are equipotential lines and how do they help to understand the electric field?
How is electric charge stored?

Key Terms

Static electricity - The buildup of electric charge on the surface of objects.
Proton - A subatomic particle with a positive electrical charge.
Electron - A subatomic particle with a negative electrical charge.
Conductor - A material in which charges move freely.
Insulator - A material in which charge cannot move freely.
Induction - The process of charging a conductor by bringing it near another charged object.
Coulomb's Law - States that electric force is proportional to the product of two charges and inversely proportional to the square of the distance between them.
Electric field - A region around a charged object that determines the force exerted on nearby charged objects.
Electric field lines - Lines pointing in the direction of the electric force on a positive test charge placed near a charged object.
Electric potential - The electric potential energy per unit charge.
Potential difference - The difference in electric potential between two points that indicates the work that must be performed against electric forces to move a charge between the two points in question divided by the charge.
Equipotential Line - A line, perpendicular to the electric field, along which a charge will have zero potential difference between any two points and will require zero work to move between those points.
Capacitor - A device that can store electric charge, and consists of two conducting objects (usually plates or sheets) placed near each other but not touching.
Law of Conservation of Charge - Any process for which the net amount of electric charge produced is zero.

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