Preview Objectives Properties of Electric Charge Transfer of Electric Charge Chapter 16 Section 1 Electric Charge

Chapter 16 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.

Chapter 16 Section 1 Electric Charge Properties of Electric Charge There are two kinds of electric charge. –like charges repel –unlike charges attract Electric charge is conserved. –Positively charged particles are called protons. –Uncharged particles are called neutrons. –Negatively charged particles are called electrons.

Click below to watch the Visual Concept. Visual Concept Chapter 16 Section 1 Electric Charge Electric Charge

Chapter 16 Section 1 Electric Charge Properties of Electric Charge, continued 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). One Coulomb is approx. 6 million trillion electrons or protons. The fundamental unit of charge, e, is the magnitude of the charge of a single electron or proton. e = x 10 –19 C

Properties of Charge Add pic of atom Electrical forces join atoms into molecules. Electric charge is a fundamental property of matter. Protons are tiny, but relatively massive. Electrons are 1/2000 the mass of protons. The negative charge on every electron has exactly the same magnitude as the positive charge on every proton.

Properties of Charge Protons join with neutral particles (via a nonelectrical force) to make positively charged atomic nuclei. Positive nuclei attract electrons, which move in a “quantum cloud” about the nucleus. Atoms are electrically neutral – the number of electrons is equal to the number of protons. Chemical properties of an atom are determined by the number of electrons, hence by the number of protons – atomic number.

Properties of Charge Atoms can bond with other atoms electrically to make molecules. Sometimes they “share” electrons and sometimes atoms give-up electrons to create ions which are charged. The force of an electric charge decreases as distance increases between charges. In other words, an electric charge creates an electric field in the space around it. Other charges experience forces from this electric field when they encounter this field. This is similar to the gravitational field.

Electric Force vs. Gravitational Force Electric force is very strong – some 40 powers of 10 stronger than the gravitational force. Consider: Gravitational Constant = 6.673x Electrical Force Constant = 8.99x10 9 The constant for electrical force is much larger than the gravitational constant.

Electric Force vs. Gravitational Force There are two kinds of electric force, hence this allows for neutral “bonds” of matter and negates the obvious electric nature of matter. Even though the gravitational force is relatively weak, there is one kind of gravitational force and the massive Earth exhibits substantial gravitational force. In other words, there is not another force “canceling” out the perceived effects of the gravitational force.

Electrical Charge – Everyday Applications Paint shops Printers and copiers Pollution control systems Electric strike to your car

Chapter 16 Section 1 Electric Charge Transfer of Electric 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.

Chapter 16 Section 1 Electric Charge Transfer of Electric Charge, continued 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.

Click below to watch the Visual Concept. Visual Concepts Visual Concept Chapter 16 Charging by Induction

Chapter 16 Section 1 Electric Charge Transfer of Electric Charge, continued 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.

Preview Objectives Coulomb’s Law Sample Problem Chapter 16 Section 2 Electric Force

Chapter 16 Objectives Calculate electric force using Coulomb’s law. Compare electric force with gravitational force.

Chapter 16 Coulomb’s Law Two charges near one another exert a force on one another called the electric force. Coulomb’s law states that the electric force is propor- tional to the magnitude of each charge and inversely proportional to the square of the distance between them. Section 2 Electric Force

Coulomb’s Law, continued The Coulomb force is a field force. A field force is a force that is exerted by one object on another even though there is no physical contact between the two objects. Chapter 16 Section 2 Electric Force

Chapter 16 Section 3 The Electric Field Electric Field Strength An electric field is a region where an electric force on a test charge can be detected. The SI units of the electric field, E, are newtons per coulomb (N/C). The direction of the electric field vector, E, is in the direction of the electric force that would be exerted on a small positive test charge.

Chapter 16 Section 3 The Electric Field Electric Field Strength, continued Electric field strength depends on charge and distance. An electric field exists in the region around a charged object. Electric Field Strength Due to a Point Charge

Moving Electric Charge