An electric field is said to exist in a region of space if an electric charge placed in that region is subject to an electric force.

An electric line of force is a line so drawn that a tangent to it at any point indicates the orientation of the electric field at that point.

Lines of force originate at the surface of a positively charged body and terminate at the surface of a negatively charged body.

A line of force shows the direction in which a positive test charge would be accelerated in that part of the field.

The electric field intensity is proportional to the number of lines of force per unit area normal to the field.

The electric field intensity, E, at any point in an electric field is the force per unit positive charge at that point.

E = F/q

E is electric field intensity in newtons per coulomb, N/CF is the force in Newtonsq is the test charge in coulombs

The force on a 10 C charge is 7 Newtons. What is the magnitude of the electric field?

An electrostatic charge is placed in an electric field that has an intensity of 1.50 x 105 N/C. The charge experiences a force of 2.10 N. Calculate the magnitude of the charge in C.

SinceE = F/q andF = kq1q2/d2,then E = F/q = kq1q2/qd2.

E = kq1q2/qd2

The test charge q cancels out and E = kq/d2.

E = kq/d2

This is the formula for the electric field strength at a distance “d” produced by a point charge “q”.This field strength is a vector.

What is the electric field 0.5 m from a 7 C charge? What is the direction of the field?

What is the electric field 0.4 m from a -3 C charge? What is the direction of the field?