AP Physics C: Mechanics : Understanding Electrostatics

Study concepts, example questions & explanations for AP Physics C: Mechanics

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Example Questions

Example Question #1 : Electricity And Magnetism Exam

Four particles, each of charge , make up the four corners of a square with equal side lengths of . For the charge in the top left corner of the square, in what direction is the net force that it experiences due to its interactions with the other three particles? 

Possible Answers:

Directly to the left

Directly to the right

 upwards of left

 downwards of right

Correct answer:

 upwards of left


The correct answer is 45 degrees upwards of left. Since all particles have charge , all forces will be repulsive (there will be no attracting forces). The particle in the top-right corner creates a repulsive force directly to the left, and the particle in the bottom-left corner creates a repulsive force directly upwards. These are equal in magnitude, since they are both at distance  from the top left corner. The bottom-right corner also creates a repulsive force, but acts along the same direction as the vector sum of a leftwards and upwards force.

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