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G19-3a. Solving Net Electric Force Problems

The following table provides a list of the important components of setting up net force problems.

Always draw a force diagram. Draw the forces extending from the charge on which you're finding the net electric force. Give the forces approximately correct relative magnitudes.
For labeling electric forces, use the double subscript notation, Fab, where the a subscript represents the charge on which the force acts and the b subscript represents the charge producing the force.
Always show your +x- and y-axes.
When doing a net force problem, your force diagram may only show forces. Don't show fields on a force diagram.
Write a net force equation for each axis. Write the forces as magnitudes and introduce signs to indicate directions.
When substituting Coulomb's Law for electric force, substitute the absolute values of the charges.

 

Below are example problem solutions.

Finding the position between two positive charges where the net force on a third, positive charge is 0

Finding the net electric force on a charge due to two other charges (2-dimensional symmetric arrangement)



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