Direct Current Circuits

The terminal voltage of a battery will be…

less than the emf (electromotive force) when the battery is providing a current to an external circuit

Electromotive Force

The maximum possible voltage the battery can provide between its terminals

The current delivered by a battery

The value of the emf, the total load resistance, and the internal resistance

I = (epsilon)/R+ r

Resistors in series (equation)

The sum of the resistances of the individual resistors:
Req = R1 + R2 + R3

Resistors in parallel (equation)

The total resistance is the inverse of the sum of the inverses

1/Req = 1/R1 + 1/R2 + 1/R3

Kirchoff’s rules

The procedure for analyzing more complex circuits

Junction rule

At any junction, the sum of the currents must equal zero

Loop rule

The algebraic sum of the potential difference across all circuit elements around any closed loop must equal zero.

Currents entered into the junction are entered as _____, whereas currents directed out are entered as ____

+1; -1

Charges move from the high potential end of a resistor toward the low potential end. So a resistor traveling in the direction of the current has a potential difference of what?

-IR

Charges move from the high potential end of a resistor toward the low potential end. So a resistor traveling in the direction opposite the current has a potential difference of what?

+IR

If a source of emf is traversed in the direction of the emf (from neg → to pos), the potential difference is what?

+(epsilon)

If a source of emf is traversed in the direction opposite the emf (pos → neg), the potential difference is what?

-(epsilon)

Charging a capacitor in series with a resistor involves a parameter called what?

the time constant (tau)

Charging a capacitor in series with a resistor (equation)

q(t) = C(epsilon)[1-e^-t/RC]