Electric charge and field, Guías, Proyectos, Investigaciones de Física Avanzada

¡Descarga Electric charge and field y más Guías, Proyectos, Investigaciones en PDF de Física Avanzada solo en Docsity!

18.4 Electric Field: Concept of a Field Revisited Contact forces, such as between a baseball and a bat, are explained on the small scale by the interaction of the charges in atoms and molecules in close proximity. They interact through forces that include the Coulomb force. Action at a distance is a force between objects that are not close enough for their atoms to “touch.” That is, they are separated by more than a few atomic diameters. For example, a charged rubber comb antracts neutral bits of paper from a distance via the Coulomb force. It is very useful to think of an object being surrounded in space by a force field. The force field carries the force to another object (called a test object) some distance away. Concept of a Field A field is a way of conceptualizing and mapping the force that surrounds any object and acts on another object at a distance without apparent physical connection. For example, the gravitational field surrounding the earth (and all other masses) represents the gravitational force that would be experienced if another mass were placed at a given point within the field. ln the same way, Ine Coulomb Torce field surrounding any charge extends Inroughout space. Using Caulomb's law, F =klg1g/r*, ts megritude is given by the equetian F = MgGl/r?, tor a point charge [a particie having a chesge (9) acting ona test charge q ata distance r (see Figure 18-20). Both e magrítude and direction ol the Coulomb force held deperd an (Y ard the test charge q. e Q % (a) F Fa Q % (b) Figure 18:20 The Coulomé force field dee to a positive charge: () is shows acting 00 teo diflerent charges. Both charges are the same distance trom (). (a) Since 1 5 postive, the torce | acing on is repulsivo. (bj The charge 5 is regale and geoaces in magnitude fan q)| ¿and so the force Fs acóng onit's atractivo and sironger man FF, ¿The COJO eco Mad ES US NO UNIQUE al ar PONE ln Space, DECaUSe lt depends 0 a test Cnapes q), and qy aswelas ne crarge Ta simplty Ihings, we would prefes to have a field nat depends only on Q and not on the test charge q. The electric held is defined in such á manner that represents only he charge creating it and is unique al every point in space. Specifically, the eseciric held EE is defined ho be Ine ratio al e Couloenib force lo the test charge: E=E 194) mese E is the electrostatic force (ar Coulomb force) exened on a positive test charge q. Itis undersiood hal E is in e same direction as Fl is also assumed Ihal y is so small that il does nol alter the charge distribution creating the esectric held. The uns ol edectric held are newions per 'coLÉOmb [NIC]. 11 Me elec melc is known, én Ie elecirastalic force on any charge q is simply oblseed by muliplying charge mes electric Meta, or F = E. Consider the elecaic held due to a poira charge (. According to Coulomb's len the force it exerts on a test charge q is F=kigQl!r” Tus ne magnitude ol the elecuc field, E, for a point charge is (1512) lA 88] al. Ei a Since the test cheege cancela, we ses tal