🔍 Key Concepts

• Capacitance in AC vs DC circuits – how a capacitor behaves differently when voltage is steady versus when it is changing • Relationship between voltage and current in a capacitor – current flow depends on the rate of change of voltage (dV/dt) • Which component resists change in voltage vs change in current – compare capacitor and inductor behavior

💭 Think About

• Think about what happens to the voltage across a capacitor if you try to change it suddenly. What does the capacitor "do" in response? • In a purely DC circuit, what happens to current after a capacitor is fully charged? How is that different in AC where voltage is constantly changing direction and magnitude? • Which device is used to smooth or filter rapid voltage changes in power supplies: a capacitor or an inductor?

✅ Before You Answer

• Make sure you know which device resists change in current (that’s not the capacitor) and which resists change in voltage • Eliminate any options that sound like diode behavior, such as allowing current in only one direction or rectifying current • Ask whether the correct property would still make sense for a sinusoidal AC voltage that is always changing, not steady like DC