Electric Field Lines - a “map” of the strength of the electric field. The electric field is...
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Transcript of Electric Field Lines - a “map” of the strength of the electric field. The electric field is...
![Page 1: Electric Field Lines - a “map” of the strength of the electric field. The electric field is force per unit charge, so the field lines are sometimes called.](https://reader036.fdocuments.net/reader036/viewer/2022062308/56649e685503460f94b64646/html5/thumbnails/1.jpg)
Electric Field Lines - a “map” of the strength of the electric field. The electric field is force per unit charge, so the field lines are sometimes called lines of force.
![Page 2: Electric Field Lines - a “map” of the strength of the electric field. The electric field is force per unit charge, so the field lines are sometimes called.](https://reader036.fdocuments.net/reader036/viewer/2022062308/56649e685503460f94b64646/html5/thumbnails/2.jpg)
Electric field lines are always directed away from positive charges and toward negative charges. Where lines are closest together, the electric field is strongest.
![Page 3: Electric Field Lines - a “map” of the strength of the electric field. The electric field is force per unit charge, so the field lines are sometimes called.](https://reader036.fdocuments.net/reader036/viewer/2022062308/56649e685503460f94b64646/html5/thumbnails/3.jpg)
Where the electric field lines are equally spaced, the electric field has the same strength at all points.
![Page 4: Electric Field Lines - a “map” of the strength of the electric field. The electric field is force per unit charge, so the field lines are sometimes called.](https://reader036.fdocuments.net/reader036/viewer/2022062308/56649e685503460f94b64646/html5/thumbnails/4.jpg)
Two separated point charges that have the same magnitude but opposite signs are called an electric dipole.
![Page 5: Electric Field Lines - a “map” of the strength of the electric field. The electric field is force per unit charge, so the field lines are sometimes called.](https://reader036.fdocuments.net/reader036/viewer/2022062308/56649e685503460f94b64646/html5/thumbnails/5.jpg)
The electric field of a dipole is proportional to the product of the magnitude of one of the charges and the distance between the charges. This product is called the dipole moment.
![Page 6: Electric Field Lines - a “map” of the strength of the electric field. The electric field is force per unit charge, so the field lines are sometimes called.](https://reader036.fdocuments.net/reader036/viewer/2022062308/56649e685503460f94b64646/html5/thumbnails/6.jpg)
Electric field lines always begin on a positive charge and end on a negative charge and do not start or stop in midspace.Also, the number of lines leaving a positive charge or entering a negative charge is proportional to the magnitude of the charge.
![Page 7: Electric Field Lines - a “map” of the strength of the electric field. The electric field is force per unit charge, so the field lines are sometimes called.](https://reader036.fdocuments.net/reader036/viewer/2022062308/56649e685503460f94b64646/html5/thumbnails/7.jpg)
Field lines never cross, because at any one point there is only one value for the electric field.
![Page 8: Electric Field Lines - a “map” of the strength of the electric field. The electric field is force per unit charge, so the field lines are sometimes called.](https://reader036.fdocuments.net/reader036/viewer/2022062308/56649e685503460f94b64646/html5/thumbnails/8.jpg)
Excess electrons within a conductor are repelled by all electrons in the material. Due to the distance factor of Coulomb’s law, 1/r2, they rush to the surface of the conductor.
![Page 9: Electric Field Lines - a “map” of the strength of the electric field. The electric field is force per unit charge, so the field lines are sometimes called.](https://reader036.fdocuments.net/reader036/viewer/2022062308/56649e685503460f94b64646/html5/thumbnails/9.jpg)
They spread out evenly over the surface (They repel each other also). An excess positive charge also moves to the surface of a conductor.
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At equilibrium under electrostatic conditions, any excess charge resides on the surface of a conductor.
![Page 11: Electric Field Lines - a “map” of the strength of the electric field. The electric field is force per unit charge, so the field lines are sometimes called.](https://reader036.fdocuments.net/reader036/viewer/2022062308/56649e685503460f94b64646/html5/thumbnails/11.jpg)
Free electrons within the conductor are not moving, so no electric field exists there. At equilibrium under electrostatic conditions, the electric field at any point within a conducting material is zero.
![Page 12: Electric Field Lines - a “map” of the strength of the electric field. The electric field is force per unit charge, so the field lines are sometimes called.](https://reader036.fdocuments.net/reader036/viewer/2022062308/56649e685503460f94b64646/html5/thumbnails/12.jpg)
Additionally, the conductor shields any charge within it from electric fields created outside the conductor. Electronic circuits are often protected from “stray” electric fields by metal containers.
![Page 13: Electric Field Lines - a “map” of the strength of the electric field. The electric field is force per unit charge, so the field lines are sometimes called.](https://reader036.fdocuments.net/reader036/viewer/2022062308/56649e685503460f94b64646/html5/thumbnails/13.jpg)
A conductor alters the electric field around it.
The electric field just outside the surface of a conductor is perpendicular to the surface at equilibrium under electrostatic conditions.
![Page 14: Electric Field Lines - a “map” of the strength of the electric field. The electric field is force per unit charge, so the field lines are sometimes called.](https://reader036.fdocuments.net/reader036/viewer/2022062308/56649e685503460f94b64646/html5/thumbnails/14.jpg)
If the field were not perpendicular, there would be a component parallel to the surface which would make the free electrons move over the surface; but the electrons do not move, so the field must be perpendicular.
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An electric field is sometimes produced by charges spread out over a region, not by a single point charge. An extended collection of charges is called a charge distribution.
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Gauss’ law describes the relationship between a charge distribution and the electric field it produces.Gauss law for a point
charge is: EA = q/ε0
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EA = q/ε0
E is electric field magnitudeA is the area of the surfaceq is the charge in coulombs ε0 is the permittivity of free space
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The product of electric field magnitude E and the area of the surface A, EA is called the
electric flux, E. E = EA.
This definition for flux only works for a point charge and a spherical Gaussian surface.
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The Gaussian surface can have any arbitrary shape, but it must be closed. The field direction is not necessarily perpendicular to the surface.
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The magnitude of the electric field need not be constant on the surface, it can vary from point to point.
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By dividing the surface into many small sections, finding the flux for each section, and adding them together, the total flux of the surface can be found.
E = ∑(E cos)∆A
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Gauss’ law relates the electric flux E to the net charge q enclosed by the arbitrarily shaped Gaussian surface.
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Gauss’ lawThe electric flux through a Gaussian surface is equal to the net charge q enclosed by the surface divided by the ε0 , the permittivity of free space:
E = ∑(E cos)∆A = q/ε0.
The SI unit of electric flux: N•m2/C
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Ex. 14 - A thin spherical shell has radius R. A positive charge Q is spread uniformly over the shell. Find the magnitude of the electric field at any point (a) outside the shell and (b) inside the shell.
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Ex. 15 - Use Gauss’ law to prove that the electric field inside a parallel plate capacitor is constant and has a magnitude E = /ε0. is the charge density on a plate.
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