Moving a positive test charge through a uniform electric field, you must do work. What energy change occurs for the test charge?

Moving a positive test charge through a uniform electric field, you must do work. What energy change occurs for the test charge?

• A. No energy changes
• B. Potential energy decreases
• C. Kinetic energy increases only
• D. Potential energy increases

Answer: (D)

When a positive test charge moves in a uniform electric field, its electric potential energy changes with position: moving against the field to a region of higher potential requires you to do work. The work you perform increases the charge’s electric potential energy by the amount of work done (ΔU = W_ext). If you move slowly so the kinetic energy stays essentially the same, the net energy transfer goes entirely into raising potential energy. So the energy change is an increase in potential energy. Moving with the field would have increased kinetic energy and decreased potential energy, but the situation here specifies you must do work, which raises potential energy.

When a positive test charge moves in a uniform electric field, its electric potential energy changes with position: moving against the field to a region of higher potential requires you to do work. The work you perform increases the charge’s electric potential energy by the amount of work done (ΔU = W_ext). If you move slowly so the kinetic energy stays essentially the same, the net energy transfer goes entirely into raising potential energy. So the energy change is an increase in potential energy. Moving with the field would have increased kinetic energy and decreased potential energy, but the situation here specifies you must do work, which raises potential energy.