1. An electric field describes a region where an electric charge will experience a force if placed in that region.
The electric field can be represented by field lines. These lines start on a positive charge and end on a negative charge.
The direction of the field lines show the direction of the electrostatic force that would act on a positive charge, q,
if you placed it there.

2. Electric field lines never cross and are drawn perpendicular to a surface.
The electric field is stronger where the field lines are closer together.

4. The Electric Field is defined as the force acting on a positive test charge (q), divided by the charge: E E F F
Electric field of a point charge +Q r

6. A proton is released in a uniform electric field, and it experiences an electric force of 3.75 × N toward the south. What are the magnitude and direction of the electric field? E +
south F

7. An electric field is defined as being present in any region where a charged object experiences an electric force. 

9. 4) E-fields add as vectors
Notes on E-field
1) The E-field points in the direction of force on a positive test charge
2) If a negative charge were placed in the E-field, what do you suppose would happen?
3) The E-field is a property of the fixed charges only (it is independent of the test charge)
4) E-fields add as vectors
5) Given the E-field value at a certain point, we can calculate the force F on any charge q0 placed there:
F = q0E
© Laura Fellman

15. What are the magnitude and direction of the electric field at a point midway between a +7.0 mC and a -8.0 mC charge 8.0 cm apart? Assume no other charges are nearby. + - d q1 q2 E1 E2

16. Four charges are placed in a square. There is a - 20
Four charges are placed in a square. There is a micro-coulomb charge placed at the (0 cm, 0 cm) mark, a 81.2 micro- coulomb charge placed at the (0 cm, 40.6 cm) mark, a micro-coulomb charged placed at the ( 40.6 cm, 40.6 cm) mark, and a micro-coulomb charge placed at the ( 40.6, 0cm) mark.
Determine the strength of the electric field in the center of the square.