Electric Fields

Charge (Q):  

Charge is determined by the number of elementary charges (e); measured in Coulombs (C).

Coulomb:      1C = 6.2 x 10¹⁸ e

Elementary Charge (e): 

The elementary charge is one + or - charge equal to the amount of charge on a proton or on an electron (e = 1.6 x 10^-19C)

Total Charge (Q):

                    Q = Ne   (N = # of elementary charges)

Electric Field (E):

E-field direction is away from positive (toward negative).  Its direction is defined by the direction of the force on a positive test charge. 

Example 1:

Example 2:

Example 3:

Example 4:   Sketch the field lines around 2 charges of the same sign.

E-Field due to a Point Charge:

The magnitude of the E-field is defined as the electric force per unit charge (in N/C).

     E = F_e/Q

where  F_e= kQQ/R²

so     E = kQ/R²

The E-Field produced by 2 or more charges is the VECTOR sum of each individual force:

E = E₁ + E₂ + ...

***Note: Do not simply add the numbers.  The vector direction MUST be considered for each vector which may mean a triangle or component consideration.