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I. The Lead Acid Electric Battery. Sulfuric Acid Electrolyte:. -. +. Terminals. Oxidation at the Negative Plate (Electrode:Anode):. Sulfuric Acid Solution H 2 SO 4. Spongy Lead (Pb). Lead Oxide (PbO 2 ). Reduction at the Positive Plate (Electrode:Cathode):. Cell: 2 V
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I The Lead Acid Electric Battery Sulfuric Acid Electrolyte: - + Terminals Oxidation at the Negative Plate (Electrode:Anode): Sulfuric Acid Solution H2SO4 Spongy Lead (Pb) Lead Oxide (PbO2) Reduction at the Positive Plate (Electrode:Cathode): Cell: 2 V Battery: Multiple cells
Kirchoff’s Rules • Conservation of charge • Junction (Node) Rule: At any junction point, the sum of all currents entering the junction must equal the sum of the currents leaving the junction. • Conservation of energy • Loop Rule: The some of the changes in potential around any closed path of a circuit must be zero.
Series Circuit Apply the Loop Rule +
Parallel Circuits + Apply the Junction Rule
Rule Set – Problem Solving Strategy • A resistor transversed in the direction of assumed current is a negative voltage (potential drop) • A resistors transversed in the opposite direction of assumed current is a positive voltage (potential rise) • A battery transversed from – to + is a positive voltage. • A battery transversed from + to - is a negative voltage. • Ohm’s Law applies for resistors. • Both the loop rule and junction rule are normally required to solve problems.
More about the Loop Rule • Traveling around the loop from a to b • In (a), the resistor is traversed in the direction of the current, the potential across the resistor is – IR • In (b), the resistor is traversed in the direction opposite of the current, the potential across the resistor is is + IR
Loop Rule, final • In (c), the source of emf is traversed in the direction of the emf (from – to +), and the change in the electric potential is +ε • In (d), the source of emf is traversed in the direction opposite of the emf (from + to -), and the change in the electric potential is -ε
Example Problem 1 Given: V = 3 Volts Find: current in each resistor
Example Problem 2 Given: Find: current in the 20 W resistor
AC Power ?
Charging a capacitor in an RC circuit Same Symbol At t = 0, Qo = 0 and
Solving the charging differential equation Kirchoff’s loop rule Convert to a simple equation in Current by taking the first derivative w.r.t. time Separate variables
Discharging the capacitor in an RC circuit At t = 0, Q = Qo
Solving the discharging differential equation Kirchoff’s loop rule Separate variables Integrate
Electrical Safety • Current kills, not voltage (70 mA) • Normal body resistance = 105W But could be less than 1000 W • Take advantage of insulators, remove conductors • Work with one hand at a time • Shipboard is more dangerous • Electrical safety is an officer responsibility