Calculating electric field intensity requires the knowledge about the current charge level of the object that is making the electric field and the distance between that charged object and the measuring tool. Electric field intensity (or strength) is a vector quantity, which means it has direction as well as magnitude. The magnitude of this intensity comes from the way it is measured.
An electric charge builds an electric field and is known as the "source charge." The intensity of this electric field can undergo measurement by any other charge that exists in the general area. A test charge measures the electric field intensity, and it has a charge expressed by the letter "q." When the test charge is set inside the electric field, a force acts on that charge, either repulsive or attractive, and this force is expressed by the letter "F." Defining the magnitude of this field requires knowing the force per charge in place. So electric field intensity equals force divided by test charge.
It is always necessary to have two charges to encounter a particular force. Within electricity, it takes two bodies to generate the repulsion or attraction response. However, the final answer regarding intensity is not dependent on the size of the test charge.