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, using conservation of charge, why capacitors in series all carry the same charge. (Guide: “Capacitors in combination”)
- I can explain why the equivalent capacitance of a series group is less than its smallest capacitance. (Practice Q1)
- I can describe how the charge, potential difference, current and stored energy change while a capacitor charges and while it discharges. (Guide: Figure 3; “Energy in an RC circuit”)
- I can state what the time constant means for charging (about 63%) and for discharging (about 37%). (Guide: “Charging a capacitor through a resistor”; “Discharging”)
Calculation and skills
- I can find the equivalent capacitance of a network and the charge, potential difference and energy for each capacitor. (Guide: Worked example 1; Practice Q4)
- I can derive R dq/dt + q/C = ℰ from the loop rule and solve it by separating variables. (Guide: “Charging a capacitor through a resistor”)
- I can use q(t), I(t) and ΔV_C(t) to find a value at a given time, or the time to reach a given value, using natural logs. (Guide: Worked example 2; Practice Q5)
- I can find currents just after a switch closes and after a long time in a circuit with several branches. (Guide: “Just after and long after”; Practice Q6)
- I can linearise discharge data, plot ln ΔV_C against t and find τ and an unknown C from the slope. (Guide: “Measuring a time constant”; Practice Q7)
Reasoning
- I can predict factors of change, such as the effect of doubling R on the initial current and the charging time. (Practice Q3)
- I can explain why energy decays faster than charge, and find the fraction left after a number of time constants. (Practice Q2)
- I can show that charging stores half the battery’s energy and dissipates the other half, whatever R is. (Guide: “Energy in an RC circuit”)
- I can explain how a meter’s resistance could change a measured time constant. (Practice Q7)
All ticked? You have finished Unit 11. Move on to Topic 12.1, Magnetic Fields, or return to the course roadmap.