Field lines and equipotentials
Drawing the invisible electric field with lines.
Field lines start on positive charges and end on negative charges; the tangent gives the direction of the field and the density of the lines shows its strength. All points on an equipotential surface have the same potential, and the surface is everywhere perpendicular to the field lines; the potential decreases along the direction of the field lines. The field of several charges is the vector sum of their individual fields.
This is a static model: forces and the graph update as soon as you change a parameter.
Potential along the line joining the charges
The potential goes to infinity near each charge, so the curve breaks there; the vertical line marks the midpoint between the charges.
Think about it
What is the potential on the perpendicular bisector between two equal and opposite charges?
Every point on the perpendicular bisector is equidistant from the two charges, so their potentials are equal in magnitude and opposite in sign and add up to zero; the whole bisector is therefore an equipotential line. Set q₁ = 2 μC and q₂ = −2 μC and look at the vertical equipotential in the middle.
Model assumptionsPoint charges in vacuum · Only field lines in the page plane are drawn · Number of lines proportional to charge
Data log
Set the parameters and click “Record data”. Record several rows with different parameters to plot their relationship and fit a straight line; pause and record at different times to study how a reading changes with time.