# R14 2 r13 r14 physics212lecture2slide5

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Unformatted text preview: = 2 r12 + 2 r13 + 2 r14 r12 r13 r14 q4 F1 F2,1 q3 F3,1 F4,1 F3,1 q4 F1 F2,1 q1 F kq E1 ≡ q = r 1 1 ˆ r+ 2 2 12 12 kq3 kq ˆ ˆ r13 + 24 r14 2 r13 r14 Physics 212 Lecture 2, Slide 5 Physics 212 Lecture 2, Slide Electric Field “Electric fields and also their use with lines of charge really confuse me! “ “How fields add together“ F E≡ q The electric field E a t a p o int in s p a c e is s im p ly th e fo rc e p e r unit c h a rg e a t th a t p o int. Ele c tric fie ld d ue to a p o int c h a rg e d p a rtic le Superposition Qi ˆ E = ∑ k 2 ri ri i Q ˆ E=k 2r r q2 E4 E2 Field points toward negative and away from positive charges. E E3 q4 q3 08 Physics 212 Lecture 2, Slide 6 Physics 212 Lecture 2, Slide Checkpoint 1 “Field directions were confusing.” Field Two equal, but opposite charges are place on the x axis. The positive charge is placed to the left of the origin and the negative charge to the right, as shown in the figure above. What is the direction of the electric field at point A? A. Up B. Down C. Left D. Right E. Zero 09 What is the direction of the electric field at point B? A. Up B. Down C. Left D. Right E. Zero simulation Physics 212 Lecture 2, Slide 7 Physics 212 Lecture 2, Slide Checkpoint 2 In which of the two cases below is the magnitude of the electric field at the point labeled A the largest? E E “The magnitudes are equal, only the direction is The different. Case one is down and to the right while case two is up and to the right.” while 12 same Physics 212 Lecture 2, Slide 8 Physics 212 Lecture 2, Slide Two Charges Two charges q1 and q2 are fixed at points (­a,0) and (a,0) as shown. Together they produce an electric field at point (0,d) which is directed along the negative y­ axis. y (0,d) E (­a,0) q1 q2 (a,0) x Which of the following statements is true: a) b) c) d) 22 Both charges are negative Both charges are positive The charges are opposite There is not enough information to tell how the charges are related Physics 212 Lecture 2,...
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