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The electric field lines for a configuration of two charges are shown. There are at least two features of importance in the diagram. First, some of the electric field lines are drawn from one source charge to the other source charge. And second, the number of field lines surrounding each source is the same number.
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Direction of Electric Field Lines:
Electric field lines are drawn to portray information about the strength and the direction of an electric field in the space surrounding a source charge. The electric field direction at a location about a source charge is the direction which a positive test charge would be pushed or pulled when placed at that location. Thus, electric field lines point in the direction which a positive test charge would be pushed or pulled.
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Density of Electric Field Lines and Field Strength:
Electric field lines are drawn to portray information about the strength and the direction of an electric field in the space surrounding a source charge. The density of lines at a given location - their closeness to each other - represents information about how strong the electric field is at that location. Wherever the lines are dense (close together), the electric field is strong. If a given source charge has many lines surrounding it, one would reason that the electric field is strong about that source and thus the source charge possesses a relatively high quantity of charge.
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If electric field lines are drawn for a configuration of two oppositely-charged sources, then a positive test charge would respond in the opposite manner to each of the source charges. That is, the positive test charge would be repelled by the positive source charge and attracted towards the negative source charge; this is the direction that the electric field lines are drawn.
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