Unit01_2_Web_Lecture_Notes

# Unit01_2_Web_Lecture_Notes - E , at the location of a test...

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Notes from lecture: 23 Jan 2008. Some of the charged particles in conductors can move freely throughout the object. Familiar conductors include metals and salt water. None of the charged particles in insulators move freely throughout the object. Familiar insulators include glass, some plastics, and very very pure water. (Warning: no common source of water is an insulator.) In the demonstration (diagram above) we saw how a charged insulator can be used to polarize a conductor. There is no net charge on the conductor, however it can still be affected by the electrostatic force. The design of an electroscope (diagram below) is based on this principle.

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In the diagram below, we say that the charge 1 q exerts a force on 2 q through 1 q ’s electric field (and vice versa). If 1 q is moved, there is a finite time before the force on 2 q changes as a result. The information about the movement of 1 q travels at the speed of light. We define the electric field
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Unformatted text preview: E , at the location of a test particle with a small charge q to be q F E q ← ≡ . The test charge q is defined such that it doesn’t disturb the original charge distribution associated with the electric field. The SI units for electric fields are N/C. The electric field of any charge distribution is a vector field. Consider a single particle with charge q (below). Since the magnitude of the force on a test charge > q due to q is 2 4 1 r q q F q ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ = ← πε . The magnitude of the electric field, due to q , at the location of the test charge q , which is some distance r from q , is 2 4 1 r q E ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ = . Note that this does not depend on q . Like electrostatic force, the electric field obeys the principle of superposition. For a distribution of n charges n E E E E + + + = L 2 1 total , where i E is the electric field due to the i th charge....
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## This note was uploaded on 05/15/2008 for the course PHYS 2208 taught by Professor Fulbright, r during the Spring '07 term at Cornell.

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Unit01_2_Web_Lecture_Notes - E , at the location of a test...

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