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Unformatted text preview: Physics 51 Sample Midterm Exam #1 (23 points) by Todd Sauke Question #1. A point charge Q = -800 nC (nano- Coulombs) and two unknown point charges, q 1 and q 2 , are placed as shown in the figure at right. The electric field at the origin O, due to charges Q, q 1 and q 2 , is equal to zero. We want to determine the values of charges q 1 and q 2 . The electric field vector at the origin has two components (x and y). Because the electric field at the origin is zero, both the x and y components are zero. We can consider the x and y components separately. Remember that the y component of the electric field at the origin due to q 1 is zero, since it is on the x axis. What is the y component of the E field at the origin due to the charge Q? (Use a trigonometric function to obtain the y component.) _______________________________ N/C 1 point (check the sign!) What must be the y component of the E field at the origin due to q 2 (in order to cancel out the E field from Q)? ________________________________N/C 1 point What must the charge q 2 be to provide this field? _________________________________nC 1 point (note units!) Working similarly, what must the charge q 1 be in order for the E field at the origin to be zero?...
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