1. Time constant Is the time it takes for V (or I) to change by 63% of its value If C is large, more charge can be stored, so takes longer to fill/empty. More R in the circuit means smaller current, so longer to fill/empty. A cap is considered fully charged or discharged after 3 time constants Charging: Discharging:

2. LO: sketch and explain the graphs for charging a capacitor It’s easy at first because the plates are empty, but as they fill the stored charge starts to repel further charge and the rate decreases Voltage across capacitor t V max Current in circuit t I max As the rate of charge movement decreases, the current flow in the circuit decreases

3. LO: sketch and explain the graphs for discharging a capacitor The voltage will be at a max to begin with, drops quickly at first (due to maximum repulsion), but then more slowly as fewer charges remain on the capacitor. The current will be large at first, but decrease as potential left to “push” decreases Voltage across capacitor t V max Current in circuit t I max

4. 1) Read p243 – 246 2) Look at Example on p245 3) Do Activity 14C Learning Tasks: Hātarei, 26 Hakihea 2015 H/W booklets: Q8-14 Due: Monday 8 th September Then:

5. Do now: NCEA 2006 1) Calculate the total capacitance 2) Calculate the total charge stored in the capacitors 3) Calculate the total energy stored in the capacitors 4) Calculate the voltage across the 4.00 μF capacitor Hātarei, 26 Hakihea 2015