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HR22_post

# HR22_post - Register your iclicker The following 20...

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Register your iclicker • The following 20 iclickers are not registered yet 1024784C, 10276156, 1029E6DF, 102A3A00, 103F7659, 103FB798, 1040D080, 10457520, 1045DA8F, 10463167, 1067A8DF, 1068E29A, 1 1069CBB2, 107A83E9, 10A306B5, 19513179, 1C874DD6, 1FB6993, AADF255, FF1CD33 • Check if the one is yours and register asap

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Chapter 22 Electric Fields • Will introduce the concept of an electric field ( symbol ) • The following topics will be covered Electric field generated by a point charge Using the principle of superposition determine the electric field created by a collection of point charges as well as continuous charge distributions Assuming that the electric field at a point P is known, E r 2 calculate the electric force on any charge placed at P Define the notion of an electric dipole . Determine the net force , the net torque , exerted on an electric dipole by a uniform electric field As long as charges are stationary Coulomb’s law describes adequately the forces among charges. If the charges are not stationary we must use an alternative approach by introducing the electric field
The Electric Field Coulomb’s law tells us that a charged particle q 1 acts on charged particle q 2 placed near particle 1 (at a distance) 1 2 2 1 4 o q q F r πε = Question: How does particle 2 “know” of the presence of particle 1 ? How can there be “action at a distance”? 3 Answer is that particle 1 sets up an electric field in the space surrounding it. The particle 2 “knows” of the presence of particle 1 because it is affected by the electric field that particle 1 has created The idea of electric field was introduced by Michael Faraday in 19 th century Charge q 1 barb2right generates electric field barb2right exerts a force on q 2 E r F r

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Definition of the Electric Field Consider the positively charged rod (Fig.a). For every point P in the vicinity of the rod we define the electric field vector as follows: 1. We place a positive “test charge” q 0 at point P 2. We measure the electrostatic force exerted on q 0 by the charged rod 3. We define the electric field vector at point P as E r F r 4 From the definition it follows that Note: We assume that the “test charge” q 0 is small enough so that its presence at point P does not affect the charge distribution on the rod and thus alter the electric field vector we are trying to measure 0 q F E r r = F E r r ↑↑ SI Units: N/C
Electric Field Lines Consider a sphere of an uniform negative charge . If we place a positive charge near the sphere, an electrostatic force pointing toward the center of the sphere will act on the charge. Thus, the electric field vectors at all points near the sphere are directed radially toward the sphere A way to visualize patterns in electric fields Spreading of electric field lines with distance 5 from the sphere tells us that the magnitude of the electric field decreases with the distance If the sphere were of uniform positive charge , the electric field vectors at all points would be directed radially away from the sphere. Thus

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