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 current as the rate at which charge crosses a cross-section, and state that 1 A = 1 C/s. (Guide: “What current measures”)
- I can explain that a potential difference (emf) drives charge round a circuit by setting up a field in the conductor. (Guide: “What current measures”)
- I can describe the random motion and the slow drift of free electrons, and explain why zero current does not mean the carriers are at rest. (Guide: “Drift velocity”; Practice Q1)
- I can explain why current has a direction but is not a vector, while current density is a vector. (Guide: “The direction of current”; Practice Q3)
- I can state the direction of conventional current and explain why electrons in a wire drift the opposite way. (Practice Q5, Q7)
Calculation and skills
- I can use I = dq/dt, and find charge from q = ∫I dt or the area under an I–t graph. (Practice Q4)
- I can derive I = nqv_dA from a sketch of carriers crossing a section. (Guide: Figure 1; Practice Q7)
- I can calculate drift speed, current density and the field E = ρJ, with correct units. (Guide: Worked example 1; Practice Q5)
- I can find a total current by integrating a non-uniform J over rings of area 2πr dr. (Guide: Worked example 2; Practice Q6)
Reasoning
- I can predict how drift speed changes when the wire’s diameter changes at fixed current. (Practice Q2)
- I can explain why a lamp lights at once even though the drift speed is tiny. (Guide: Worked example 1)
- I can explain why I = JA gives the wrong answer when J varies across a wire. (Practice Q6)
All ticked? Move on to Topic 11.2, Simple Circuits.