College Physics III – Thermodynamics, Electricity, and Magnetism
Definition
Electric force is the attractive or repulsive interaction between any two charged objects. It is governed by Coulomb's Law, which states that the magnitude of the force between two point charges is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.
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Electric force can be attractive (between opposite charges) or repulsive (between like charges).
The formula for electric force is given by $F = k \frac{q_1 q_2}{r^2}$, where $k$ is Coulomb's constant ($8.99 \times 10^9 \text{Nm}^2/\text{C}^2$), $q_1$ and $q_2$ are the magnitudes of the charges, and $r$ is the distance between them.
Electric forces obey Newton's Third Law: The force on charge $q_1$ due to charge $q_2$ is equal in magnitude and opposite in direction to the force on charge $q_2$ due to charge $q_1$.
The superposition principle applies: The total electric force on a charge due to multiple other charges is the vector sum of the individual forces exerted by each of those charges.
In a uniform electric field, a positive test charge experiences a force in the direction of the field, while a negative test charge experiences a force opposite to it.
Review Questions
What determines whether an electric force between two charges is attractive or repulsive?
How does doubling one of the charges affect the magnitude of the electric force between two point charges?
Explain how electric forces adhere to Newton's Third Law.
Related terms
Coulomb's Law: A fundamental principle quantifying the amount of electrostatic force that one point charge exerts on another. It states that this force is proportional to the product of their charges and inversely proportional to the square of their separation distance.
Electric Field: A region around a charged particle where other charged particles experience an electric force. It is defined as electric force per unit charge.
The potential energy stored in a system of charged particles due to their positions relative to each other. This energy depends on both magnitudes and signs of interacting charges as well as their distances apart.