Unit 2 Electrical Quantities and Ohm’s Law

1. Unit 2 Electrical Quantities and Ohm’s Law Objectives: • Define a coulomb. • Define an ampere. • Define a volt. • Define an ohm. • Define a watt.

2. Unit 2 Electrical Quantities and Ohm’s Law Objectives: • Compute electrical values using Ohm’s law. • Discuss basic types of circuits. • Use the Ohm’s wheel charts.

3. Unit 2 Electrical Quantities and Ohm’s Law A coulomb is a quantity measurement for electrons. One coulomb contains 6.25 x 1018 electrons, or 6,250,000,000,000,000,000 electrons.

4. Unit 2 Electrical Quantities and Ohm’s Law The ampere is a measurement of the amount of electricity that is flowing through a circuit. One ampere (A) is defined as one coulomb of electricity flowing past a given point in one second.

5. Unit 2 Electrical Quantities and Ohm’s Law Compare and contrast these two systems.

6. Unit 2 Electrical Quantities and Ohm’s Law There are two theories about current flow. Electron flow theory describes current flow from negative to positive. Conventional current flow theory states electrical current flows from positive to negative.

7. Unit 2 Electrical Quantities and Ohm’s Law Conventional current flow theory and electron flow theory.

8. Unit 2 Electrical Quantities and Ohm’s Law Electrons moving from atom to atom.

9. Unit 2 Electrical Quantities and Ohm’s Law Electrical sources are divided into two basic types: • Direct Current (DC) which is unidirectional (one way).     • Alternating Current (AC) which is bidirectional (two way, or back and forth).    

10. Unit 2 Electrical Quantities and Ohm’s Law A complete path must exist before electricity can flow through a circuit. A circuit with a complete path for electrical flow is called a closed circuit. If the circuit path is incomplete or broken, this is called an open circuit.

11. Unit 2 Electrical Quantities and Ohm’s Law A simple switch closes and opens an electrical circuit.

12. Unit 2 Electrical Quantities and Ohm’s Law A shortcircuit has an unintended shorter pathway.

13. Unit 2 Electrical Quantities and Ohm’s Law The basic principle of the instantaneous effect of electric impulses.

14. Unit 2 Electrical Quantities and Ohm’s Law The impulse of electricity can travel faster than light. It would take light 1.3 seconds to travel around the earth 10 times. If a wire were wrapped around the earth 10 times, when the switch was closed the light would come on almost instantly.

15. Unit 2 Electrical Quantities and Ohm’s Law A volt or voltage is electrical pressure.

16. Unit 2 Electrical Quantities and Ohm’s Law An ohm is the unit of resistance or opposition to the flow of electricity.

17. Unit 2 Electrical Quantities and Ohm’s Law The watt is the unit of electrical power.

18. Unit 2 Electrical Quantities and Ohm’s Law Force equals flow rate times pressure.

19. Unit 2 Electrical Quantities and Ohm’s Law Amperes times volts equals watts.

20. Unit 2 Electrical Quantities and Ohm’s Law Common power units.

21. Unit 2 Electrical Quantities and Ohm’s Law Ohm’s law states that in a DC (Direct Current) circuit, the current is directly proportional to the voltage and inversely proportional to the resistance. E(volts) = I(amps) x R(ohms)

22. Unit 2 Electrical Quantities and Ohm’s Law Ohm’s Law Symbols: P is the symbol for Watts. E is the symbol for Volts. I is the symbol for Amperes. R is the symbol for Resistance or Ohms.

23. Unit 2 Electrical Quantities and Ohm’s Law Ohm’s Law states that it takes one volt to push one ampere through one ohm. E = Volts E = I x R R = Resistance I = Amps

24. Unit 2 Electrical Quantities and Ohm’s Law Using the Ohm’s law chart. I = E / R E = I x R R = E / I

25. Unit 2 Electrical Quantities and Ohm’s Law Adding P (watts) to the Ohm’s law chart. P = E2 /R P = E x I P = I2 x R I = I = P / E I = E / R E = E = I x R E = P / I R = E / I R = P / I2 R = E2 / P

26. Unit 2 Electrical Quantities and Ohm’s Law Remember: E = EMF, or voltage I = intensity of current, or amperage R = resistance in ohms P = power in watts E(volts) = I(amperes) x R(ohms) P(watts) = I(amperes) x E(volts)

27. Unit 2 Electrical Quantities and Ohm’s Law

28. Unit 2 Electrical Quantities and Ohm’s Law Metric Units

29. Unit 2 Electrical Quantities and Ohm’s Law • Review: • A coulomb is a quantity measurement of electrons. • An ampere (A) is one coulomb per second. • Either the letter I, which stands for intensity of current flow, or the letter A, which stands for amperes, can be used in Ohm’s law formulas.

30. Unit 2 Electrical Quantities and Ohm’s Law • Review: • Voltage is referred to as electric pressure, potential difference, or electromotive force. An E or a V can be used to represent voltage in Ohm’s law formulas. • An ohm (Ω) is a measurement of resistance (R) in an electric circuit.

31. Unit 2 Electrical Quantities and Ohm’s Law • Review: • The watt (W) is a measurement of power in an electrical circuit. It is represented by either a W or a P (power) in Ohm’s law formulas. • Electric measurements are generally expressed in engineering notation.

32. Unit 2 Electrical Quantities and Ohm’s Law • Review: • Engineering notation differs from the standard metric system in that it uses steps of 1000 instead of steps of 10. • Before current can flow, there must be a complete circuit. • A short circuit has little or no resistance.