Physics Lec 6 PDF

Physics By: Dr. Engy Ragaei Abdelmaksoud E-mail: [email protected]  Contents Mechanics Electricity & Magnetism 1. Physics and measurements 1. Electric Force 2. Motion in one dimension 2. Electric Field 3. Vectors 3....

Physics By: Dr. Engy Ragaei Abdelmaksoud E-mail: [email protected]  Contents Mechanics Electricity & Magnetism 1. Physics and measurements 1. Electric Force 2. Motion in one dimension 2. Electric Field 3. Vectors 3. Capacitance 4. Motion in two dimensions 4. Voltage, Current, Resistance 5. Laws of motion 5. Magnetic Fields, Induction 6. Work and Energy Oscillations & Waves 1. Oscillatory Motion 2. Wave Motion Lecture 6  Objectives 1. Electric Fields [Chapter 23] ▪ Properties of Electric Charges ▪ Coulomb’s Law ▪ The Electric Field ▪ Electric Field Lines ▪ Motion of a Charged Particle in a Uniform Electric Field  Properties of Electric Charges Static electricity  Properties of Electric Charges Static electricity ▪ On a dry day when you walk across a carpeted room wearing socks. Charge is transferred between the carpet and your socks and between your socks and your body. ▪ Electrons were transferred from the carpet to your socks and your body, so they built up a negative charge. ▪ When touching the doorknob, the charges suddenly jumped to the metal, creating the feeling of getting shocked. Properties of Electric Charges  Properties of Electric Charges Types of Charge ▪ Electric charge is not created by these processes; it is just transferred from one object to another. ▪ The law of conservation of charge The net charge of a closed system never changes. ▪ There are two kinds of electric charges, which were given the names positive and negative by Benjamin Franklin (1706–1790). ▪ Electrons are identified as having negative charge, and protons are positively charged. ▪ Charges of the same sign repel one another and charges with opposite signs attract one another.  Properties of Electric Charges ▪ A neutral atom has equal numbers of protons and electrons, a balance of positive and negative charge. ▪ If the number of electrons and protons is not equal, then the atom is called an ion and has a nonzero net charge. ▪ If the ion has more electrons than protons, its net charge is negative; if the ion has fewer electrons than protons, its net charge is positive.  Properties of Electric Charges Charging Objects by Friction Induction Conduction Physical contact No Physical contact Physical contact Non Conductors Conductors Conductors eˋs transfers No eˋs transfers eˋs transfers  Properties of Electric Charges Charging Objects by Friction  Properties of Electric Charges Charging Objects by Induction  Properties of Electric Charges Charging Objects by Induction  Properties of Electric Charges Charging Objects by Conduction  Coulomb’s law ▪ The electric force (sometimes called the electrostatic force) between two stationary charged particles. ▪ The magnitude of the electric force (sometimes called the Coulomb force) between two point charges is given by Coulomb’s law. Coulomb’s law Coulomb’s law Coulomb’s law Coulomb’s law Coulomb’s law Coulomb’s law Coulomb’s law The Electric Field The Electric Field The Electric Field The Electric Field The Electric Field The Electric Field The Electric Field The Electric Field  Electric Field Lines Notice that the lines become closer together as they approach the charge, indicating that the strength of the field increases as we move toward the source charge.  Electric Field Lines ▪ The electric field lines for two point charges of equal magnitude but opposite signs (an electric dipole). ▪ Because the charges are of equal magnitude, the number of lines that begin at the positive charge must equal the number that terminate at the negative charge.  Electric Field Lines ▪ The electric field lines in the vicinity (‫ )ﺑﺠﻮار‬of two equal positive point charges. ▪ The lines are nearly radial at points close to either charge, and the same number of lines emerges from each charge because the charges are equal in magnitude. ▪ At great distances from the charges, the field is approximately equal to that of a single point charge of magnitude 2q.  Electric Field Lines ▪ The electric field lines associated with a positive charge +2q and a negative charge –q. ▪ The number of lines leaving +2q is twice the number terminating at -q. ▪ Only half the lines that leave the positive charge reach the negative charge. The remaining half terminate on a negative charge we assume to be at infinity. ▪ At distances much greater than the charge separation, the electric field lines are equivalent to those of a single charge +q. Motion of a Charged Particle in a Uniform Electric Field Motion of a Charged Particle in a Uniform Electric Field Motion of a Charged Particle in a Uniform Electric Field Motion of a Charged Particle in a Uniform Electric Field