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 explain how E = ∫ k dq/r² r̂ comes from adding the fields of many point charges (superposition). (Guide: “From point charges to continuous charge”)
- I can explain why I must add components, not magnitudes, when the dE vectors point in different directions. (Guide: “Common misconceptions”; Practice Q1)
- I can use symmetry to state the direction of E for a ring on its axis, a rod on its bisector and an arc at its centre. (Guide: “Symmetry does half the work”; Practice Q6)
- I can say when a point-charge model or an infinite-line model is a good approximation for a finite rod. (Practice Q5)
Calculation and skills
- I can write dq = λ dx or dq = λR dθ, with the correct λ for a rod or an arc. (Guide: “From point charges to continuous charge”)
- I can derive E for a finite rod at a point on its own line and evaluate it with numbers. (Guide: Worked example 1; Practice Q2)
- I can derive E for a finite rod on its perpendicular bisector and take the infinite-line limit, λ/(2πε₀r). (Guide: “The finite rod on its perpendicular bisector”; Practice Q5)
- I can derive E on the axis of a ring and find where it is greatest. (Guide: Worked example 2; Practice Q4)
- I can derive E at the centre of a semicircle or part of one by integrating over θ. (Guide: “Arcs”; Practice Q3, Q6)
- I can set up the integral for a rod whose charge density varies along it. (Practice Q7)
Reasoning
- I can check a result by showing it becomes kQ/r² far from the object. (Guide: Worked examples 1 and 2; Practice Q7)
- I can sketch E along the axis of a ring, showing zero at the centre, the maximum and the sign change. (Guide: Figure 2)
- I can compare the fields of two charge arrangements and explain the difference in size or direction. (Practice Q3, Q6, Q7)
All ticked? Move on to Topic 8.5, Electric Flux, or return to the course roadmap.