University of Technology Lecturer1 Dr. Haydar AL-Tamimi

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University of Technology Lecturer: Dr. Haydar AL-Tamimi 1 Coulombs Law and Electric Field Intensity 2.1 Coulomb’s law Coulomb stated that the force between two very small objects separated in a vacuum or free space by a distance, which is large compared to their size, is proportional to the charge on each and inversely proportional to the square of the distance between them, or 𝐹 = 𝑄 1 𝑄 2 4𝜋𝜖 0 𝑅 2 (𝟏) here 𝑄 1 and 𝑄 2 are the positive or negative quantities of charge, 𝑅 is the separation, and 𝜖 0 is called the permittivity of free space and has magnitude, measured in farads per meter (F/m), 𝜖 0 = 8.854 × 10 −12 = 1 36𝜋 × 10 −9 F/m (𝟐) In order to write the vector form of (2), we need the additional fact (furnished also by Colonel Coulomb) that the force acts along the line joining the two charges and is repulsive if the charges are alike in sign or attractive if they are of opposite sign. Let the vector 𝑟 1 locate 𝑄 1 , whereas 𝑟 2 locates 𝑄 2 . Then the vector 𝐑 𝟏𝟐 = 𝑟 2 − 𝑟 1 represents the directed line segment from 𝑄 1 to 𝑄 2 , as shown in Figure 2.1. The vector F 2 is the force on 𝑄 2 and is shown for the case where 𝑄 1 and 𝑄 2 have the same sign....