Unit 2 Electrical Quantities and Ohm s Law

Transcription

1 Electrical Quantities and Ohm s Law

2 Objectives: Define a coulomb. Define an ampere. Define a volt. Define an ohm. Define a watt.

3 Objectives: Compute electrical values using Ohm s law. Discuss basic types of circuits. Use the Ohm s wheel charts.

4 A coulomb is a quantity measurement for electrons. One coulomb contains 6.25 x electrons, or 6,250,000,000,000,000,000 electrons.

5 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.

6 Compare and contrast these two systems.

7 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.

8 Conventional current flow theory and electron flow theory.

9 Electrons moving from atom to atom.

10 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).

11 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.

12 A simple switch closes and opens an electrical circuit.

13 A short circuit has an unintended shorter pathway.

14 The basic principle of the instantaneous effect of electric impulses.

15 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.

16 A volt or voltage is electrical pressure.

17 An ohm is the unit of resistance or opposition to the flow of electricity.

18 The watt is the unit of electrical power.

19 Force equals flow rate times pressure.

20 Amperes times volts equals watts.

21 Common power units.

22 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)

23 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.

24 Ohm s Law states that it takes one volt to push one ampere through one ohm. E = I x R I = E / R R = E / I E = Volts I = Amps R = Resistance

25 Using the Ohm s law chart. E = I x R I = E / R R = E / I

26 Adding P (watts) to the Ohm s law chart. P = E 2 / R P = E x I P = I 2 x R I = P R I = P / E I = E / R R = E / I R = P / I 2 R = E 2 / P E = PR E = I x R E = P / I

27 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)

28 Metric Units

29

30 Review: 1. A coulomb is a quantity measurement of electrons. 2. An ampere (A) is one coulomb per second. 3. 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.

31 Review: 4. 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. 5. An ohm (Ω) is a measurement of resistance (R) in an electric circuit.

32 Review: 6. 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. 7. Electric measurements are generally expressed in engineering notation.

33 Review: 8. Engineering notation differs from the standard metric system in that it uses steps of 1000 instead of steps of Before current can flow, there must be a complete circuit. 10. A short circuit has little or no resistance.