EGR 1011 Egr 101 Batteries Introduction to Ohms Law

EGR 1012 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 1013 Circuit Components Batteries + +

EGR 1014 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 charge move toward the positive charge and a current is produced The amount of current is constrained by the resistance of the circuit

EGR 1015 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 1016 Current Direction We will adopt “Conventional Flow” for all of our work!

EGR 1017 Mathematical Relation 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 1018 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.

Solution V = E/Q I = dQ/dt Q = E/V dQ/dt = (dE/dt)/V V = 10 Volts dE/dt = 2 Joules/sec I = 2/10 Amperes = 0.5 A EGR 1019

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

Series Circuits A series circuit is one in which the same current flows through each element of the circuit. EGR 10111

Voltage Sources in Series Voltage sources in series add algebraically = 4.5 V EGR 10112

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

Voltage Sources in Series Voltage sources in series add algebraically (-1.5) = 1.5 V EGR 10114

EGR In Class Activity What is the total voltage between terminals A and B in the figure below? Which terminal is at a higher potential? 9V4V15V AB

Units Current I in Amperes, e.g. 1.2 A Voltage V in Volts, e.g. 6 V Resistance R in Ohms, e.g. 5 Ω EGR 10116

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

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

EGR Determine the Current + _ I

EGR Determine the Voltage + _

EGR Determine the Resistance + _