Work through the list without notes. If you cannot do a statement, follow its link, then come back. Guide = study guide; Practice = practice questions.
Understanding
- I can define the electric potential energy of two charges as the external work needed to bring them slowly from infinitely far apart. (Guide: “Energy stored in a system of charges”)
- I can explain why U_E belongs to the system of charges and not to one charge. (Guide: “Energy stored in a system of charges”)
- I can explain what a positive or a negative U_E says about a pair of charges, and why negative energy is allowed. (Guide: “The equation and its sign”; Practice Q3, Q6d)
Calculation and skills
- I can calculate U_E = kq₁q₂/r for a pair of charges, keeping their signs and using metres. (Guide: Worked example 1; Practice Q1)
- I can predict the factor by which U_E changes when the charges or the separation change, without mixing it up with the force. (Guide: “Predicting changes”, Worked example 3; Practice Q2)
- I can sketch U_E against r for like and unlike charges on the same axes. (Guide: Figure 1; Practice Q6a)
- I can list every pair in a system of three or four charges and add their energies. (Guide: Worked example 2; Practice Q4, Q5)
- I can find the external work to assemble, separate or rearrange charges from W_ext = ΔU_E. (Guide: “Work done to rearrange charges”; Practice Q5b, Q6c)
Reasoning
- I can explain the sign of the external work from the forces between the charges. (Practice Q5c)
- I can explain why total U_E can be zero even though forces act. (Guide: “Common misconceptions”)
- I can use the decrease in U_E to find the kinetic energy of released charges. (Practice Q7)
All ticked? Move on to Topic 10.5, Electric Potential, or return to the course roadmap.