Unit 11 Electrostatics: Electric Charges and Force

Electric Force Between Two Charges

• The magnitude of the force (F) between two electric charges (q₁ and q₂) separated by a distance (r) is given by: F = k * q₁q₂ / r², where k is a constant of proportionality.
• The value of k depends on the system of units used and the medium between the charges.
• The electric charges are assumed to be point or localized charges, provided the size of the bodies carrying the charges is very small compared to the distance between them.

Direction of the Force

• To show the direction of the force, a unit vector (î) is used, pointing from the charge q₁ towards the charge q₂.
• The force exerted by charge q₁ on charge q₂ in vector form is: F₁₂ = k * q₁q₂ / r² â.
• The force exerted by charge q₂ on charge q₁ in vector form is: F₂₁ = k * q₁q₂ / r² â.

Force Exerted Between Charges

• The force exerted by charge q₁ on q₂ is conventionally denoted by F₁₂.
• The force exerted by charge q₂ on q₁ is conventionally denoted by F₂₁.
• F₁₂ = -F₂₁, implying that the force exerted by one charge on the other is equal in magnitude but opposite in direction.