Electric Charge and Electric Field

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1 Chapter 21 Electric Charge and Electric Field PowerPoint Lectures for University Physics, Thirteenth Edition Hugh D. Young and Roger A. Freedman Lectures by Wayne Anderson

2 En este Chapter 21, usted prodrá Conocer la naturaleza de la charge eléctrica y su conservation Diferenciar las formas de cargar los objetos Usar la ley de Coulomb para calcular fuerza eléctrica entre partículas cargadas Diferenciar entre campo eléctrico y fuerza eléctrica Calcular campo eléctrico debido a un conjunto de cargas Usar líneas de campo eléctrico para visualizar el campo eléctrico Calcular las propiedades de los dipolos eléctricos

Introduction El agua hace posible la vida, en ella se disuelven las moléculas biológicas esenciales. Qué propiedades eléctricas la hacen tan buen solvente?

3 Introduction El agua hace posible la vida, en ella se disuelven las moléculas biológicas esenciales. Qué propiedades eléctricas la hacen tan buen solvente? La fuerza elcgtromagnetica, una de las cuatro fuerzas fundamental Se inicia con los conceptos de carga y campo eléctrico. El fenómeno de la electrostática data desde la antiguedad (600 AC)

4 Electric charge Ley de cargas: cargas del mismo signo se repelen; cargas de signos contrarios se atraen. Figure 21.1 below shows some experiments in electrostatics.

5 Laser printer A laser printer makes use of forces between charged bodies.

6 Carga Electrica y la estructura de la materia Un electrón es la unidad elemental de carga pero en el sistema MKS se asume como unidad fundamental de carga al Coulomb (C), que tiene un orden de magnitud de cargas elementales

7 Atoms and ions A neutral atom has the same number of protons as electrons. A positive ion is an atom with one or more electrons removed. A negative ion has gained one or more electrons.

8 MÉTODOS DE ELECTRIZACIÓN Frotamiento Contacto Inducción Electrostática Polarización

9 Conductors and insulators A conductor permits the easy movement of charge through it. An insulator does not. Most metals are good conductors, while most nonmetals are insulators. (See Figure 21.6 at the right.) Semiconductors are intermediate in their properties between good conductors and good insulators.

10 Charging by induction In Figure 21.7 below, the negative rod is able to charge the metal ball without losing any of its own charge. This process is called charging by induction.

11 Electric forces on uncharged objects The charge within an insulator can shift slightly. As a result, two neutral objects can exert electric forces on each other, as shown in Figure 21.8 below.

12 Preguntas para taller Cuál es la definición de cuerpo cargado? Como se puede electrizar una cuerpo, o porción de materia? Hacer un mapa conceptual sobre los métodos de electrización Aplicación de los métodos de electrización electrostáticos en la construcción de maquinas electróstáticas

13 Máquinas Electrostáticas Maquinas Electrostáticas de Von Guericke

14 Máquinas Electrostáticas LA MÁQUINA DE VAN MARUM

15 Máquinas Electrostáticas 1883 MÁQUINA ELECTROSTÁTICA DE WIMSHURST 1929 GENERADOR VAN DER GRAFFf

16 Electrostatic painting Induced positive charge on the metal object attracts the negatively charged paint droplets.

17 Coulomb s law Coulomb s Law: The magnitude of the electric force between two point charges is directly proportional to the product of their charges and inversely proportional to the square of the distance between them. (See the figure at the right.) Mathematically: F = k q 1 q 2 /r 2 = (1/4π 0 ) q 1 q 2 /r 2

Measuring the electric force between point charges The figure at the upper right illustrates how Coulomb used a torsion balance to measure the

18 Measuring the electric force between point charges The figure at the upper right illustrates how Coulomb used a torsion balance to measure the electric force between point charges. Example 21.1 compares the electric and gravitational forces. Follow it using Figure at the lower right.

19 Force between charges along a line Read Problem-Solving Strategy Follow Example 21.2 for two charges, using Figure at the right. Follow Example 21.3 for three charges, using Figure below.

20 Vector addition of electric forces Example 21.4 shows that we must use vector addition when adding electric forces. Follow this example using Figure below.

Electric field A charged body produces an electric field in the space around it (see Figure 21.

21 Electric field A charged body produces an electric field in the space around it (see Figure at the lower left). We use a small test charge q 0 to find out if an electric field is present (see Figure at the lower right).

22 Definition of the electric field Follow the definition in the text of the electric field using Figure below.

23 Electric field of a point charge Follow the discussion in the text of the electric field of a point charge, using Figure at the right. Follow Example 21.5 to calculate the magnitude of the electric field of a single point charge.

24 Electric-field vector of a point charge Follow Example 21.6 to see the vector nature of the electric field. Use Figure at the right.

25 Electron in a uniform field Example 21.7 requires us to find the force on a charge that is in a known electric field. Follow this example using Figure below.

26 Superposition of electric fields The total electric field at a point is the vector sum of the fields due to all the charges present. (See Figure below right.) Review Problem-Solving Strategy Follow Example 21.8 for an electric dipole. Use Figure below.

27 Field of a ring of charge Follow Example 21.9 using Figure below.

28 Field of a charged line segment Follow Example and Figure below.

29 Field of a uniformly charged disk Follow Example using Figure below.

30 Field of two oppositely charged infinite sheets Follow Example using Figure below.

31 Electric field lines An electric field line is an imaginary line or curve whose tangent at any point is the direction of the electric field vector at that point. (See Figure below.)

Electric field lines of point charges Figure 21.

32 Electric field lines of point charges Figure below shows the electric field lines of a single point charge and for two charges of opposite sign and of equal sign.

33 Electric dipoles An electric dipole is a pair of point charges having equal but opposite sign and separated by a distance. Figure at the right illustrates the water molecule, which forms an electric dipole.

34 Force and torque on a dipole Figure below left shows the force on a dipole in an electric field. Follow the discussion of force, torque, and potential energy in the text. Follow Example using Figure below right.

35 Electric field of a dipole Follow Example using Figure

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