Competency #8
Answer and Explanation
Based on Coulomb's Law, rank the following sets of particles from greatest electrical repulsive force to least electrical repulsive force. Note: p + represents a proton and e - represents an electron.
The correct answer is: C=D>A>B.
A. 
B. 
C. 
D. 
Coulomb's Law is:
In this problem, there are two types of charges. The protons and electrons have nominal charges of +1 and –1, respectively. A repulsive force will be felt between any two like charges. Therefore, each set of particles above will experience a repulsive force.
Since all of the charges are the same size (differing only in sign) and all the forces are repulsive, we can look just at the distance. The electric force is inversely proportional to the distance squared. That is, the farther apart the particles, the lower the electrical force. Since the particles in C and D are equally far apart, they experience the same size electric repulsive force. The particles in B are farthest apart and experience the smallest electric repulsive force.