Where Does Current Come From? The free electrons in a conductor need to be replaced when they move through the conducting medium (the wire). These electrons are replaced by electrons from a source of energy such as a battery. EGR 101

Circuit Components Batteries + + EGR 101

Source of Voltage in a Battery A chemical reaction within the battery separates positive and negative ions (charged atoms) When the battery is connected to a circuit, the negative charges move toward the positive terminal and a current is produced The amount of current is constrained by the resistance of the circuit EGR 101

Example of A Battery The source of energy E in (Joules) releases charges Q in (Coulombs) Voltage (V) – the difference in potential that uses E = one Joule (J) of energy to move a charge Q = one coulomb (C). EGR 101

Current Direction We will adopt “Conventional Flow” for all of our work! EGR 101

Mathematical Relationship E: Energy required to move charges in Joules (J). Q: Charge value in Coulombs (C). V: Voltage or potential difference across the battery's posts in volts (V). Thus, V = E / Q. In units: 1 Volt = 1 Joule/Coulomb EGR 101

Team In-class Activity (15 minutes) A 10 V source uses 2 Joules of energy per second. Calculate the current being used by the source. Hint, turn the word problem into equations; write down what you know. V = 10 = w (J)/Q (C); P = 2 W = 2 J/s Solving for Q gives Q = W/V Then substituting into I = Q/t gives I = W/(V*T) = 2/10 = 1/5 A EGR 101

When batteries are connected with their polarities in the same direction, they are in a series-aiding arrangement. EGR 101

opposite direction, they are in a series-opposing arrangement. When batteries are connected with their polarities in the opposite direction, they are in a series-opposing arrangement. EGR 101

In Class Activity What is the total voltage between terminals A and B in the figure below? Which terminal is at a higher potential? A B 9V 4V 15V EGR 101

Introduction to Ohm’s Law A 1 Ohm resistance limits the current to 1 Amp when 1 Volt is applied. V = I.R EGR 101

Ohm’s Law Three forms: Use the form that best describes the quantity that you are trying to determine EGR 101

Determine the Current I + _ EGR 101

Determine the Voltage + _ EGR 101

Determine the Resistance + _ EGR 101