Resistance Notes (Text pg. 553-563)

• The amount of current flow in a circuit depends on two things: the potential difference of the power supply, and the nature of the pathway through the loads that are using the electric potential energy.
• Electrical resistance is the measure of the opposition to current flow.
• The voltage/current (V/I) ratio is constant, and therefore must be the resistance of a load because it remained unchanged through the course of the experiment.
• As a result the equation for resistance is: R=V/I, where R is resistance in Ω (ohm), V is the potential difference in volts (V), and I is the resulting current in amperes (A).
• Ohm's Law states that the V/I ratio was constant for a particular resistor.
• Many factors that affect resistance: length, cross-sectional area, type of material, temperature. (pg. 557)
• Kirchhoff's current law: The total amount of current into a junction point of a circuit equals the total current that flows out of that same junction.
• Kirchhoff's voltage law: The total of all electrical potential decreases in any complete circuit loop is equal to any potential increases in that circuit loop.
• Resistances in Series - the general equation for more than 3 resistors: R[total] = R[1] + R[2] + R[3]... + R[N], where N is the total number of series resistors in the circuit. If the resistors are all the same: R[T] = NR
• Resistances in Parallel - the general equation for more than 3 resistors: 1/R[T] = 1/R[1] + 1/R[2] + 1/R[3]... + 1/R[N], where N is the total number of parallel resistors in the circuit. If the resistors are the same: R[T] = R/N