![]() ![]() This estimate of the flux gets better as we decrease the size of the patches. This is similar to the way we treat the surface of Earth as locally flat, even though we know that globally, it is approximately spherical. If we divide a surface S into small patches, then we notice that, as the patches become smaller, they can be approximated by flat surfaces. In general, when field lines leave (or “flow out of”) a closed surface, Φ Φ is positive when they enter (or “flow into”) the surface, Φ Φ is negative.Īny smooth, non-flat surface can be replaced by a collection of tiny, approximately flat surfaces, as shown in Figure 6.8. Therefore, quite generally, electric flux through a closed surface is zero if there are no sources of electric field, whether positive or negative charges, inside the enclosed volume. Therefore, if any electric field line enters the volume of the box, it must also exit somewhere on the surface because there is no charge inside for the lines to land on. ![]() The reason is that the sources of the electric field are outside the box. The magnitude of the flux through rectangle BCKF is equal to the magnitudes of the flux through both the top and bottom faces. Here, the net flux through the cube is equal to zero. The net electric flux through the cube is the sum of fluxes through the six faces. The electric flux through the other faces is zero, since the electric field is perpendicular to the normal vectors of those faces. The electric flux through the top face ( FGHK) is positive, because the electric field and the normal are in the same direction. Electric flux through the bottom face ( ABCD) is negative, because E → E → is in the opposite direction to the normal to the surface. Notice that N ∝ E A 1 N ∝ E A 1 may also be written as N ∝ Φ N ∝ Φ, demonstrating that electric flux is a measure of the number of field lines crossing a surface.įigure 6.7 Electric flux through a cube, placed between two charged plates. Electric flux is a scalar quantity and has an SI unit of newton-meters squared per coulomb ( N We represent the electric flux through an open surface like S 1 S 1 by the symbol Φ Φ. The quantity E A 1 E A 1 is the electric flux through S 1 S 1. If N field lines pass through S 1 S 1, then we know from the definition of electric field lines ( Electric Charges and Fields) that N / A 1 ∝ E, N / A 1 ∝ E, or N ∝ E A 1. To quantify this idea, Figure 6.4(a) shows a planar surface S 1 S 1 of area A 1 A 1 that is perpendicular to the uniform electric field E → = E y ^. Again, flux is a general concept we can also use it to describe the amount of sunlight hitting a solar panel or the amount of energy a telescope receives from a distant star, for example. Similarly, the amount of flow through the hoop depends on the strength of the current and the size of the hoop. As you change the angle of the hoop relative to the direction of the current, more or less of the flow will go through the hoop. The numerical value of the electric flux depends on the magnitudes of the electric field and the area, as well as the relative orientation of the area with respect to the direction of the electric field.Ī macroscopic analogy that might help you imagine this is to put a hula hoop in a flowing river. Using Coulomb’s law, \boldsymbol westward force on an electron.Figure 6.3 The flux of an electric field through the shaded area captures information about the “number” of electric field lines passing through the area. In the same way, the Coulomb force field surrounding any charge extends throughout space. 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. Concept of a FieldĪ 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. The force field carries the force to another object (called a test object) some distance away. It is very useful to think of an object being surrounded in space by a force field. 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.įor example, a charged rubber comb attracts neutral bits of paper from a distance via the Coulomb force. They interact through forces that include the Coulomb force. Explain the relationship between electrical force (F) on a test charge and electrical field strength (E).Ĭontact 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.Calculate the force exerted on a test charge by an electric field.Describe a force field and calculate the strength of an electric field due to a point charge.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |