Consider two positive charges, +q, separated by a distance of 2a.2a. The point x=r is shown in the figure

Sunday, 12 August 2018

4:04 PM

Machine generated alternative text: Question: Consider two positive charges, +q, separated by a distance of 2a. The point = r is shown in the figure. Note that r > a. In this question give expressions including co, the permitlvity of tree space. i Figure 1 _ Two identical charges q are placed a distance 2a apart One charge is placed at = —a and the other at x = a. The point x=r is to the right otx=a_ part 1) Write an expression tor the electric field at = r due to just the -eq charge located at = a. Your last answer was interpreted as follows: 0 part 2) Write an expression tor the net electric field at = r due to both the charges. Your last answer was interpreted as follows: 0 part 3) In the limit where r a, write a simplified expression tor the electric field. Your last answer was interpreted as follows: 0

 

Machine generated alternative text: Incorrect answer. Note: Your answers should be correct to 3 significant figures. Feedback tor Part 1) The electric field a distance d from a point charge is given by: In this case, d = r — a so 4TE0 47rE0 (r —a) As like charges repel, a positive test charged placed at = r would feel a force to the right. The electric field is thus in the -Fi directiom Marks for this submissiom 0.00/0.33. This submission attracted a penalty of 0.11 Feedback tor Part 2) Electric fields obey the law of superposition so: 1 47rE0 2 i 1 47rEo q r2 — 2ra+a2 +r2+2ra+a2 47rE0 q 2(r2+a2) i Marks for this submissiom 0.00/0.33. This submission attracted a penalty of 0.11 Feedback tor Part 3) In the limit r a we have that r2 a2 so r2 + a z r andr _ a2 z r2. So: 2(r2+a2) q 47rE0 (r2 _ a2 ) 2 2mE0 r2 • q 47rE0 2r2 r4 Note this is expected as it is the electric field a distance r from a point charge witn charge 2q. At large distances the separation of the charges is insignificant. Marks for this submissiom 0.00/0.33. This submission attracted a penalty of 0.11 A correct answer , which can be typed in as follows: q/ (4 (r-a)A2) T(P4a2) A correct answer , which can be typed in as follows: (rA2+aA2) ) / (rA2 - )A2) A correct answer is , which can be typed in as follows:

 

 

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