Question

Three charges are fixed in place as shown. The distance between charges +? and −? is equal to the distance between charges −3? and −? . System of 3 charges situated on 3 corners of a square pattern. Charge plus Q in the upper left corner. Charge minus Q in the upper right corner. Charge minus 3 Q in the lower right corner. Lower left corner is empty.

Identify which of the statements best describes the magnitudes of the forces exerted on charge −? by charges +? and −3? .

A. The magnitude of the force on charge −? due to charge −3? is equal to the magnitude of the force on charge −? due to charge +? .

B. The magnitude of the force on charge −? due to charge −3? is less than the magnitude of the force on charge −? due to charge +? .

C. The magnitude of the force on charge −? due to charge −3? is greater than the magnitude of the force on charge −? due to charge +? .

Answer 1

C. The magnitude of the force on charge −? due to charge −3? is greater than the magnitude of the force on charge −? due to charge +? .

force between two charges is given using coulomb's law as

F = k q₁ q₂/r²                            where q₁, q₂ are the two charges and "r" is the distance between the charges

let the length of side of the square be "r"

F₁ = magnitude of force by charge +q on -q charge = k q²/r²

F₃ = magnitude of force by charge +3q on -q charge = k (3q) q/r² = 3 k q²/r²

clearly , magnitude of force by charge +3q is three time the magnitude of force by charge +q.