Electrostatics– Terms to Know

1. Coulomb's Law - the electric force between two point charges is proportional to the product of their charges and inversely proportional to the square of their distances apart. (Defining equation: F = kQ₁Q₂/r². Where k is Coulomb's constant and has a value of approximately 9.0 x 10⁹ N•m²/C², Q₁ and Q₂ are the charges measured in coulombs and r is the distance that the charges are apart, expressed in metres.)

2. Coulomb - unit of charge. The coulomb is a derived unit and is defined in terms of the fundamental units ampere and second. By definition one coulomb is the amount of charge that flows past a point in one second if one ampere of current is flowing. Defining equation: Q = It where I is the current in amperes and t is the time in seconds.

3. Current - a flow of charge. The rate of flow of charge. Measured in amperes. (V)

4. Ampere - one ampere is defined as that current flowing in each of two long parallel wires one metre apart, which result in a force of exactly 2 x 10^-7 N/m of length of each conductor.

5. Field - A region of space that can cause forces on objects. Gravitational fields are detected using masses and electric fields may be detected using small test charges. The concept of "field" was developed to explain forces (action) at a distance where there was no apparent physical contact between the object causing the force and the object experiencing the force.)

6. Test Charge - a charge that is so small that it does not significantly affect an electric field in which it is placed.

7. Direction of an Electric Field at a Point in the Field - the direction that a small positive test charge would move initially if released at the point in the field.

8. Electric Field Lines (electric lines of force) - lines that are drawn to help visualize an electric field. (Note that regions where electric field lines converge are regions of large electric field intensity. Diverging lines indicate the field intensity is decreasing.)

9. Electric Field Strength or Intensity - the ratio of the electric force to the electric charge on a test charge at a point in the electric field. (Defining equation: E = F/q. Measured in N/C. For point charges and spherically symmetric charges ONLY: E = kQ/r² where Q is the charge and r is the distance from the charge. Analogous to the gravitational field strength, g, when discussing gravitational fields.) (V)

10. .Conservative force - a force (such as gravity or electric) where the work done in moving a body (such as a mass or charge) is independent of the path taken in the field. The work done depends only on the initial and final positions. (Note that the electric forces used in the solution of any problem in this course are conservative forces.)

11. .Electric Potential Energy - the potential energy a charge has due to its position in an electric field. (Measured in joules). (S)

12. Electric Potential (or Potential) - the potential energy per unit charge; the ratio of work done against an electric field or done by the field to the charge on a positive test charge when it is moved from infinity to a point in the field. If the work done against the field the potential is positive and if the field does the work on the charge (charge gains kinetic energy) the potential is negative. (Defining equation: V = W/Q. Measured in volts.). (S)

13. Volt - the unit of electric potential or potential difference. 1 V = 1 J/C.

14. Potential Difference - the difference in potential between two points in an electric field. (Defining equation: ∆V = V₂ - V₁, where the subscripts refer to two different positions in the field.) (S)

15. Voltage - the same as potential difference. Measured in volts. (S)