Three point charges are fixed along the x–axis at the following positions: charge A…
PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
Three point charges are fixed along the x–axis at the following positions: charge A (magnitude +2q) at x=0cm, charge B (magnitude −q) at x=4cm, and charge C (magnitude +3q) at x=10cm. A student wishes to analyze the electric interactions involving charge B only and chooses not to perform explicit numerical calculations.
(a) Rank the magnitudes of the electric forces exerted
• on charge B by charge A (FBA) and
• on charge B by charge C (FBC)
from greatest to least. Use the symbols “>”, “=”, or “<” for your ranking.
(b) Provide a clear qualitative justification for your ranking, explicitly discussing both the magnitudes of the interacting charges and the distances involved.
(c) Determine the direction of the net electric force acting on charge B. Explain your reasoning in terms of the individual force directions.
(d) Suppose charge A is replaced by a charge of magnitude −2q at the same location. State whether the magnitude of the net force on charge B would increase, decrease, or remain the same compared to part (c). Justify your answer qualitatively.