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Circuits

• Series combination of resistors: The equivalent resistance is R = R1 + R2 + …
• Parallel combination of resistors: If R1, R2, … are connected in parallel, the equivalent resistance R is such that 1/R = 1/R1 + 1/R2 + …
• RC circuit: Connect a battery with emf E, a resistor with resistance R, and a capacitor with capacitance C, and a switch. When the switch is open, no charge flows and the capacitor remains uncharged. If the switch is closed at time t = 0, the capacitor begins charging. The charge on the capacitor, as a function of time t, is given by Q = CE [1 – exp(-t / RC)]. The product RC has the units of time and is called the time constant of the RC circuit.