Identify the charge and distance from the charge required for the electric field calculation. For example, assume a question asks for the direction and magnitude of an electric field 1.2 meters away from a point charge of 2.0 x 10^-9 coulombs.
Substitute these values into the electric field equation. This equation identifies the electric field as the product of the electrical constant K (9.0 x 10^9 N*m^2/C^2) and the charge, q, divided by the square of the distance, d, from the charge. Thus, the calculation using the previous example would give an electric field magnitude of 7.5 newtons per coulomb.
E = (K*q ) / d^2
E = [(9.0 x 10^9 N*m^2/C^2)*(1.2 x 10^-9 C)] / (1.2^2)
E = 7.5 N/C
Identify the direction based on the charge. The electric field points outward from a positive, and inward from a negative. Thus, the example problem would have a final electric field 1.2 meters away equal to 7.5 N/C outward.