Three positive charges a, b, and c, and a negative charge d are placed in a line as shown in the diagram. all four charges are of equal magnitude. the distances between a and b, b and c, and c and d are equal.

a. which charge experiences the greatest net force? which charge experiences the smallest net force?
b. find the ratio of the greatest to the smallest net force.

a. charge C experiences the greatest net force, and charge B receives the smallest net force

b. ratio=9

Explanation:

Electrostatic Force

Two point-charges and separated a distance d will exert a force on each other of a magnitude given by the Coulomb's formula

Where k is the proportional constant of value

The diagram provided in the question shows four identical charges (let's assume their value is Q) separated by identical distance (of value d). The force between the charges next to others is

The force between charges separated 2d is

And the force between the charges A and D is

Now, let's analyze each charge and the force applied to them by the others

Let's recall equally signed charges repel each other and differently signed charges attrach each other

Charge A. It receives force to the left from B and C and to the right from D

Charge B. It receives force to the right from A and D and to the left from C

Charge C. It receives forces to the right from all charges.

Charge D. It receives forces to the left from all charges

Comparing the magnitudes of each force is just a matter of computing the fractions

a.

We can see the charge C experiences the greatest net force, and charge B receives the smallest net force

b.

The ratio of the greatest to the smallest net force is

The greatest force is 9 times the smallest net force