Drawing Field Lines

The electric field lines are parallel to the direction of force experienced by a positive test charge placed at that point.

Basic conventions when drawing field lines

  • Field lines extend out from positive charges
  • Field lines go into negative charges
  • All field lines are continuous curves or lines without breaks
  • Field lines never cross each other’s path
  • Field lines in the same direction tend to stay as far apart as possible
  • Field lines in the opposite direction tend to cancel each other
  • When electric field strength E increases (i.e. charge is stronger), the number of field lines increase
  • Field lines are always perpendicular from its source
  • Stronger field lines retain their shape better therefore are less distorted by other charges around

When 2 or more charges are placed in the vicinity of each other, the resultant E-field shape will be a combination of the individual E-field.

  • When both point charges are of the same magnitude, the shape will be symmetrical
  • When both point charges are of different magnitude, the shape will be asymmetrical

What does it mean by uniform electric field?

An uniform electric field is defined as an electric field whose influence over a charge is constant regardless of the point of the space taken into consideration.

An electric field generated by a point charge is not uniform because the electric field lines are spaced further apart as the distance from the charge increases. (The electric field gets weaker.)

electric field between parallel bars

Almost uniform E-field can be obtained with oppositely charged parallel plates when the length of the plates is much longer than the distance between them.

Electric field strength due to double and multiple point charges in space

electric field between point charges

$E_{y} = E_{1y} + E_{2y}$

$E_{x} = E_{1x} + E_{2x}$

$E = \sqrt{E_{x}^{2} + E_{y}^{2}}$


  • Resolve the electric field vectors into x and y components
  • The x and y components of the resultant electric field can be found using the first two equations above
  • The resultant electric field is then computed using the third equation

Note: If you are familiar with vectors, the resultant electric field at a point is just the vector sum of the two or more electric fields due to the charges.

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