Electric Circuits practice quiz

Key ideaI = ΔQ/Δt and R = ρL/A. Current is not used up as it goes around a circuit.

Common mistakeThinking a thicker wire has more resistance.

Key ideaIn series the current is the same and the voltages add; in parallel the voltage is the same and the currents add. Adding a parallel branch lowers the total resistance.

Common mistakeThinking adding a resistor always increases the total resistance.

Key ideaP = IV = I²R = V²/R. Use the form that matches what stays the same.

Common mistakeComparing parallel bulbs with P = I²R as if they had the same current. They share V, so use V²/R (smaller R is brighter); in series they share I, so use I²R (larger R is brighter).

Key ideaJunction rule: current in equals current out. Loop rule: the voltage changes around any closed loop add to zero.

Common mistakeSign errors: a resistor traversed along the current drops the potential by IR.

Key ideaAn uncharged capacitor acts like a wire at first; a fully charged one blocks current. After one time constant, RC, a charging capacitor has reached about 63% of its final charge.

Common mistakeLetting current flow through a fully charged capacitor.