Coulomb\'s law allows us to find the force between two point charges. Three poin
ID: 1534539 • Letter: C
Question
Coulomb's law allows us to find the force between two point charges. Three point charges are held fixed in place as shown. Consider the following comment about this situation: "There will be zero net electric force on the charge in the middle due to the other charges. Using Coulomb's law, the force due to the +Q charge is positive, and the force due to the -Q charge is negative. The forces cancel." Do you agree with this statement? Explain. How does Coulomb's law apply to situations in which there are more than two point charges? Each of the following parts involves a comparison of the net electric force exerted on a positive charge +q in two different cases. In cases A and B shown at right there are two positive point charges +Q each a distance s away from a third positive point charge +q. Is the net electric force on the +q charge in case A greater than, less than, or equal to the net electric force on the +q charge in case B? Explain. In case C, two positive point charges +2Q are each a distance s away from a third positive point charge +q. In case D, four positive point charges +Q are each a distance s away from a fifth positive point charge +q. (The angle alpha shown is the same in both cases.) Is the net electric force on the +q charge in case C greater than, less than, or equal to the net electric force on the +q charge in case D? Explain.Explanation / Answer
1) No,
In the forces did not cancel each other in the above situation. Instead they add each other.
Because: The force (FQq)on positive charge(+q) due to another positive charge(+Q) is repulsive. +Q charge repulses away the +q charge in +x-direction. Direction of force (FQq) is in positive x-direction.
The force (F-Qq)on positive charge(+q) due to negative charge(-Q) is attractive. -Q charge attracts +q charge in +x-direction. Direction of force (F-Qq) is also in positive x-direction.
Hence, by superpostion Fnet =F-Qq+FQq = non-zero.
Fnet will be zero when +q is attracted by both positive charges on two sides or negative charges i.e arrangement should be either +Q +q +Q
or -Q +q -Q
2)When there are 'n' charges are there exerting force on charge q.
Force due to each charge is calculated by Coulomb assuming there is no effect of presence of other charges on interaction of two charges.
By superposition rule : F =F1q+F2q+F3q+F4q+...+Fnq