25: Problem 25.17

INTRO:

Part A:
What is the magnitude of the net electric force on charge B in the figure?
Assume a = 2.0 cm and b = 1.3 cm .
Express your answer to two significant figures and include the appropriate units.

SOLUTION:
F_AonB= K⋅|q_A⋅q_B| / [a]² = 1/[4πϵ₀]⋅|(-1.0 nC)⋅(-2.0 nC)| / [2.0 cm]² = 4.494×10^-5N
F_ConB= K⋅|q_C⋅q_B| / ²= 1/[4πϵ₀]⋅|(2.0 nC)⋅(-2.0 nC)| / [1.3 cm]² = 2.13×10^-4N

F_NETonB = F_AonB + F_ConB = 4.494×10^-5N + 2.13×10^-4N = 2.579×10^-4N ≈ 2.6×10^-4 N

Part B:
What is the direction of the net electric force on charge B in the figure?

SOLUTION:
In the previous part, we determined the magnitude of the net force on charge B
However we must also determine the direction of the force

⇐((-)A) ((+)B) ⇐((+)C)
F_AonB is a negative charge pushing the negative charge down
F_ConB is a positive charge pulling the negative charge down

SO,
the force is directed down