1. Electronics Ohm’s Law

2. Presentation Overview • Terms and definitions • Letters and terms used in Ohm’s Law • Ohm’s Law • Use of the Ohm’s Law circle • Applications of Ohm’s Law

3. Terms and Definitions • Voltage- electrical potential; an electrical pressure created by the buildup of charge; causes charged particles to move • Volt- unit of voltage; Symbol= V • Electromotive force- ahistorical term used to describe voltage; Symbol= E • (No longer relevant, the definition of force is something that causes a mass to accelerate, and voltage or EMF does not fit that definition). E is now commonly used as a symbol for electric field strength. • Current- the flow or movement of electrons • Ampere- unit of current; Symbol= I • Resistance- opposition to current flow • Ohm- unit of resistance; Symbol= Ω(Greek symbol Omega)

4. Terms and Definitions (continued) • Energy- the fundamental ability to do work • Joule- unit of energy; Symbol= J • Electrical Power- the rate of electrical energy used in a circuit; calculated by multiplying current times voltage, or P = V • I • Watt- unit of measurement for power; a watt is one joule per second (J/s); Symbol= W • Ohm’s Law- a formula describing the mathematical relationship between voltage, current, and resistance; one of the most commonly used equations in all of science

5. Terms and Definitions (cont) • Directly proportional- having a constant ratio; a situation where one variable moves in the same direction as another variable when other conditions are constant • Inversely proportional- having a constant but inverse ratio; a situation where one variable moves in the opposite direction from another variable when other conditions remain constant • Example- current doubles when voltage is doubled if resistance is held constant; thus, voltage and current are directly proportional • Example- with a constant voltage, current decreases when resistance increases; thus, current and resistance are inversely proportional

6. Review of Letters and Terms used in Ohm’s Law • I – Electrical current in amperes • R – Resistance in ohms • V – Represents voltage in volts • A – Represents amperes • Ω– Represents ohms • E – Electromotive force (emf) in volts, sometimes used as an alternate symbol for voltage

7. Ohm’s Law • A mathematical formula typically expressed as, (Read as “current equals voltage divided by resistance.”) • This formula can be rearranged in two more ways: and

8. The Ohm’s Law Circle

9. Using The Ohm’s Law Circle • Cover the value you want to solve for • The remaining two terms give the equation

10. Example One • Solve for Current

11. Example One • Cover the current symbol

12. Example One • Cover the current symbol

13. Example One • Cover the current symbol Current equals voltage divided by resistance

14. Example Two • Solve for Voltage

15. Example Two • Cover the voltage symbol

16. Example Two • Cover the voltage symbol

17. Example Two • Cover the voltage symbol Voltage equals current times resistance

18. Example Three • Solve for Resistance

19. Example Three • Cover the resistance symbol

20. Example Three • Cover the resistance symbol

21. Example Three • Cover the resistance symbol Resistance equals voltage divided by current

22. Three Forms of Ohm’s Law 1. Calculating circuit resistance Example: R = V / I 2. Calculating circuit amperage Example: I = V / R 3. Calculating circuit voltage Example: V = IR

23. One Way To Visualize Ohm’s Law Ohm’s Law One volt is required to push one amp through one ohm resistance. E = IR Volts = Amperes x Ohms

24. Common Metric Values Ohm’s Law uses results in both large and small numbers, so a review of metric prefix values is important.

25. Practice Problem One • You have a circuit with a source voltage of 12 V DC and a circuit resistance of 150 Ω. Solve for the unknown value using Ohm’s Law.

26. Practice Problem One • You have a circuit with a source voltage of 12 V DC and a circuit resistance of 150 Ω. Solve for the unknown value using Ohm’s Law. • To solve, first write down all values V = 12 v R = 150 Ω I = ?

27. Practice Problem One • Next, look at the Ohm’s Law Circle V = 12 v R = 150 Ω I = ?

28. Practice Problem One • Cover what you are solving for V = 12 v R = 150 Ω I = ?

29. Practice Problem One • Cover what you are solving for V = 12 v R = 150 Ω I = ?

30. Practice Problem One • Cover what you are solving for V = 12 v R = 150 Ω I = ? I = 0.08 A

31. Summary of Problem One or I = 80 mA

32. Practice Problem Two • You have a circuit with a source voltage of 9 V DC and a circuit resistance of 360 Ω

33. Practice Problem Two • You have a circuit with a source voltage of 9 V DC and a circuit resistance of 360 Ω • Write down all of the values V = 9 v R = 360 Ω I = ?

34. Practice Problem Two • You have a circuit with a source voltage of 9 V DC and a circuit resistance of 360 Ω • Write down all of the values V = 9 v R = 360 Ω I = ?

35. Summary of Problem 2 V = 9 v R = 360 Ω I = ? or I = 25 mA

36. Practice Problem Three • You have a circuit with a resistance of 900 Ω and a current of 30 mA

37. Practice Problem Three • You have a circuit with a resistance of 900 Ω and a current of 30 mA R = 900 Ω I = 30 mA V = ?

38. Practice Problem Three • You have a circuit with a resistance of 900 Ω and a current of 30 mA R = 900 Ω I = 30 mA V = ?

39. Practice Problem Three • You have a circuit with a resistance of 900 Ω and a current of 30 mA R = 900 Ω I = 30 mA V = ?

40. Summary of Problem Three R = 900 Ω I = 30 mA V = ? or V = 27 v

41. Practice Problem Four I = 59 mA V = 19 v R = ?

42. Practice Problem Four I = 59 mA V = 19 v R = ?

43. Practice Problem Four I = 59 mA V = 19 v R = ?

44. Practice Problem Four I = 59 mA V = 19 v R = ?

48. Presentation Summary • Terms and definitions • Letters and terms used in Ohm’s Law • Ohm’s Law • Ohm’s law in circular expression • Use of Ohm’s Law Let’s do some problems!