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Finding magnitude of electrical field at specific point

  1. Jul 11, 2015 #1
    1. The problem statement, all variables and given/known data

    Two point-like charges are placed as shown in the figure, r1 = 28.0 cm and r2 = 56.0 cm. Find the magnitude of the electric field at point (p) shown in the figure. Let q1 = −13.0 µC, q2 = +30.0 µC.

    2. Relevant equations

    E1 = k*q1 / r^2

    3. The attempt at a solution

    The electrical field at the two points are the sum of the two electric fields of q1 and q2.

    E = E1 + E2

    The equation for E1 is:

    E1 = k*q1 / r^2

    Plugging in the known quantities:

    E1 = 8.99x10^9 *13 x10^-6 / 0.28^2

    So E1 equals

    E1 = 1492068.776 N/C

    The same process goes for E2:

    E2 = 8.99x10^9 * 30 x10^-6 / 0.56^2

    So E2 equals:

    E2 = 860012.75521 N/C

    Now adding up E1 and E1 we get:

    E = (1492.34 + 860.96) x10^3

    E = 2350701.531 N/C

    I am not sure if my reasoning is correct, if anyone can help it'll be much appreciated, thank you!
  2. jcsd
  3. Jul 11, 2015 #2


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    It is not clear from your reasoning whether or not you got the correct årocedure by luck or not. Generally, you should argue whether the fields interfere constructively or destructively, i.e., in which direction does the field from each charge point?
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