Positive (source) charges set up outward fields, which blow away positive test charges but suck in negative test charges.
Negative (source) charges set up inward fields, which suck in positive test charges but blow away negative test charges.
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Here is an worked example on how to calculate the resultant electric field strength.
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Applets:
Try setting up an electric field to guide a hockey puck to the goal
PhET Electric Hockey: Click HERE
