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21 Electric Field 1 Covering all sections
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2 Electric Charge Q = ± Ne, (N = integer) Charge of Matter q proton = +e q neutron = 0 q electron = -e Examples: He = (2p, 2n, 2e - ) charge = 0 He + = (2p, 2n, 1e - ) = +1e
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3 Like repel, Unlike attact Relative electron affinity
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4 Conductors “free” electrons electron motion = “conduction”
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5 Evidence of electron conduction away from central metallic element (gold leaf repulsion)
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6 Charging by Induction (1 of 3)
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7 Charging by Induction (2 of 3)
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8 Charging by Induction (3 of 3)
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9 attraction of an uncharged conductor
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10 “Ground” = source or sink of charge
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11 Charge re-distributes quickly after rod moves far away
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13 Example in 2D
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14 Electric Field force per charge-size [N/C]
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15 Direction of E
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16 Electric Field of a Point Charge Electric Field due to Multiple Point Charges
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17 Example: Approximating E above Uniform Line of Charge Given: 6 m long uniform strip of charge Q lies along x axis 0, 6 m. Estimate E at P = (6, 2)m by breaking strip into 3 discrete point charges q = Q/3 located at 1, 3, and 5 m along the x-axis. r1/r1 = {(6, 2) – (1, 0)}/ (29). = (5,2)/ (29) r2/r2 = (3, 2)/ (13) r3/r3 = (1, 2)/ (5)
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18 Components of Total Electric Field
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19 The net electric field at (6,2) is E = E1 + E2 + E3. E = kq(0.1855, 0.2344) angle of E = tan-1(.2344/.1855) = 51.6 . magnitude of E = kq (0.1855 2 + 0.2344 2 ) = 0.2989kq= 0.2989kQ/3 = 0.09963kQ The exact value of E = kQ/12 = 0.08333kQ
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20 Dipole – two equal size opposite sign charges at small separation distance
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21 Electric Field around a Dipole
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22 Effect of point charge on oil soaked threads
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23 Effect of two like point charges on oil soaked threads
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24 Effect of two unlike point charges on oil soaked threads
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25 EFL Conventions
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26 Force on – charge is opposite to E.
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