A student holds a small point charge and slowly moves it between two labeled points…
PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
A student holds a small point charge and slowly moves it between two labeled points inside an electrostatic field region so that its speed remains negligibly small throughout the motion. The student wonders how the work done by the electric field compares with the work done by the hand (the external agent) for different charge signs and directions of motion.
(a) For a positive test charge moved from a region of lower electric potential to a region of higher electric potential, indicate the sign (positive, negative, or zero) of the work done by (i) the electric field and (ii) the external agent. Explain your reasoning in terms of energy transfer for the charge–field system.
(b) Repeat part (a) if a negative test charge is moved through the same potential increase by the external agent at negligible speed.
(c) Using verbal descriptions only (no numerical calculations required), construct an energy bar chart for each scenario in parts (a) and (b). Your charts should explicitly show the relative magnitudes and signs of ΔKE, ΔUE (electric potential energy of the charge–field system), Wfield, and Wexternal.