Chapter 16 Section 1: Electric charge

Objectives

Understand the basic properties of electric charge.

Differentiate between conductors and insulators.

Distinguish between charging by contact, charging by induction, and charging by polarization.

Properties of electric charge

There are two kinds of electric charge. like charges repel unlike charges attract Rubbing two ballons they repel Rubbing ballon in your hair they attract

Electric charge is conserved.

Benjamin Franklin name the two different kind of charge positive and negative.

Positively charged particles are called protons. Uncharged particles are called neutrons. Negatively charged particles are called electrons

Properties of electric charge

Electric charge is quantized. That is, when an object is charged, its charge is always a multiple of a fundamental unit of charge.

Charge is measured in coulombs (C).

The fundamental unit of charge, e, is the magnitude of the charge of a single electron or proton.

e = 1.602 176 x 10–19 C

The Millikan Experiment

The Millikan Experiment

In 1909, Robert Millikan performed an experiment at the university of Chicago in which he observed the motion of tiny oil droplets between two parallel metal plates as shown in the figure above.

The oil droplets were charge by friction in an atomizer and allowed to pass trough a hole in the top plate.

Initially, the droplets fell due to their weight. The top plate was given a positive charge as the droplets fell , and the droplets with a negative charge were attracted back upward the plate.

Millikan found out that when an object is charged, its charge is always a multiple of its fundamental unit of charge, symbolize by the letter e.

Transfer of electrical charge

An electrical conductor is a material in which charges can move freely.

An electrical insulator is a material in which charges cannot move freely.

Transfer of electrical charge

Insulators and conductors can be charged by contact.

Conductors can be charged by induction.

Induction is a process of charging a conductor by bringing it near another charged object and grounding the conductor.

Transfer of electrical charge

A surface charge can be induced on insulators by polarization.

With polarization, the charges within individual molecules are realigned such that the molecule has a slight charge separation.

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