Instructions for use
This applet is designed to allow you to explore both the vector field diagram concept and the field line concept.
To get this applet to run faster on a slow computer, increase the "Speed" by upping that parameter with the button on the lower left.
To change the ratio of the charges (it is initially set to one), increase that ratio by hitting the corresponding button on the lower right.
To change the sign of one of the charges, hit the "reverse sign" button at the upper left. Red is positive charge, black is negative charge.
To move either change, click and drag on that charge.
To draw a field line through a point away from the charges, just click where you want the field line drawn.
To represent an electric field with a vector field diagram we calculate the field on a mesh of points. We show the direction of the field at every point in the mesh by putting a vector of constant length at that point. We indicate the strength of the field using color coding. In the map above, we are using red for the highest field strength, green for field strengths of intermediate values, shading to white for (and thus becoming invisible) for low field strengths.
A field line is constructed starting at any point and tracing out a line which everywhere parallel to the local field.
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