1. EGR 1011 Egr 101 Batteries Introduction to Ohms Law

2. 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.

3. EGR 1013 Circuit Components Batteries + +

4. 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

5. 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).

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

7. 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

8. 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.

9. 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. 10 When batteries are connected with their polarities in the same direction, they are in a series-aiding arrangement.

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

12. Voltage Sources in Series Voltage sources in series add algebraically 1.5 + 1.5 + 1.5 = 4.5 V EGR 10112

13. EGR 10113 When batteries are connected with their polarities in the opposite direction, they are in a series-opposing arrangement.

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

15. EGR 10115 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

16. 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

17. EGR 10117 Introduction to Ohm’s Law A 1 Ohm resistance limits the current to 1 Amp when 1 Volt is applied. V = I. R

18. EGR 10118 Ohm’s Law Three forms: Use the form that best describes the quantity that you are trying to determine

19. EGR 10119 Determine the Current + _ I

20. EGR 10120 Determine the Voltage + _

21. EGR 10121 Determine the Resistance + _