1. U3e-L2 Moving electrons have _______. The _______ of an electric circuit uses the electrons’ ability to do work. The three basic units in electricity are _________________________________. February 28, 2011 DRILL Voltage (V), Current (I), Resistance (R) Energy Load

2. Voltage (V) – the electric potential between two points of opposite charge. Voltage is the potential energy of the electrical power source. Voltage is measured in Volts (V). TERMINOLOGY U3e-L2

3. TERMINOLOGY U3e-L2 Current (I) is the rate that charges flow during a given time –Current = Charge/Time –Current is measured in ampere (amps). Amp = Coulomb/second

4. TERMINOLOGY Power source: An artifact that provides a supply of “free electrons to a circuit. A power source has a positive (+) and a negative (-) terminal. The Power Source is the origin of the Voltage in a circuit. Two types of Power Source: 1.Direct Current (DC) Power Source. Schematic symbol: 2.Alternating Current (AC) Power Source. Schematic symbol: Realistic picture

5. Power Source Symbols DC Power Source: + (Positive Terminal - Long line) - (Negative Terminal – Short line) + - This is where the symbol comes from “Wet cell”- car battery

6. Resistance (R) –a measure of the degree to which an object opposes an electric current through it. Resistance often generates heat. Resistance is measured in Ohms (  – the Greek letter Omega) TERMINOLOGY U3e-L2

7. U3e-L1 George Ohm (1789 – 1854) – a high school and university mathematics instructor Discovered ~1827 Voltage = Current x Resistance The formula: V = I x R What are the units of measure of this formula? Volts(v) = Amperes(amps.) x Ohms( Ω) Ohm’s Law Voltage Current Resistance

8. Electrical Calculations – What is Ohm’s Law? I = 3 V 2 Ω I = 1.5 amps

9. Schematics A schematic is a diagram that represents the elements of a system using symbols instead of realistic pictures. Remember: A complete circuit consists of power source, conductor, and load.

10. Schematic vs. Realistic Diagrams Which one is easier to draw? + _ Power source Conductor Load Power source Conductor Load

12. SCHEMATIC DIAGRAMS a.k.a. Schematics (+) (-) POWER SOURCE CONDUCTOR LOAD CURRENT (arrow shows the direction of electron flow) (D.C.)

13. PROBLEM SOLVING 1.Draw the diagram. 2.List the table of knowns and unknowns. 3.Write the formula. 4.Substitute. 5.Calculate. 6.Box in answer.

14. U3e-L2 An Ipod uses a 0.5 volt battery. The current in the ear bud circuit is 0.2 amperes. What is the resistance of the ear bud? Step #1 Diagram Step #2 List Information Step #3 Formula Step #4 Substitute Step #5 Solve V = 0.5v I = 0.2amps. R = ? V = 0.5 V I = 0.2amps. R = ? V = I x R 0.5 V = 0.2 A x R 2.5 Ω = R

15. U3e-L2 What voltage is needed to produce a 4 Amp circuit with a 5 Ohm resistor? Step #1 Diagram Step #2 List Information Step #3 Formula Step #4 Substitute Step #5 Solve V = ? I = 4 amp R = 5 Ohm V = ? I = 4 Amp R = 5 Ohm V = I x R V = 4 A x 5  V = 20 Volts

16. Solve the following circuit problems: (USE ALL 6 STEPS!) 1.V = 6 vI = 2 amps.R = ? 2.V = 8.5 v I = ?R = 2.125 Ω 3.V = ?I = 9 amps.R = 10 Ω 4.The heater fan on the #33 bus is on a 7 amp. circuit. The bus has a 24 v battery. What is the resistance of the fan motor?

17. U3e-L2 1)Write the given information: V = 5 volts I =.7 amps R = ? 2)Sketch a schematic diagram of the circuit: a)Start with power source b)Add conductors c)Add resistance d)Add current Problems – Ohm’s Law V = 5V I =.7A - + R = ?

18. U3e-L2 Copy the steps to solve this problem on your worksheet: 1.A cell phone charger converts the wall outlet voltage to 5 Volts to charge the cell phone. The amount of current that the charger outputs is.7 Amperes. Sketch a schematic diagram of this circuit. What is the resistance of the cell phone battery? 1)Write the given information: V = 5 volts I =.7 amps R = ? Problems – Ohm’s Law A schematic is a diagram that represents the elements of a system without using realistic pictures

19. 1)Write the given information: V = 5 volts I =.7 amps R = ? 3)Rearrange, Substitute, and Solve Problems – Ohm’s Law V = 5V I =.7A - + R = ? 2)Sketch a schematic diagram of the circuit: V = I x R R = 5V /.7A R = 7.14 W R = V / I U3e-L2

20. Electrical Power Electric Power – the rate at which electrical energy is transferred by an electric circuit. Units of power are the Watt (W) A human climbing a flight of stairs is doing work at a rate of about 200 watts. U3e-L2

21. U3e-L1 Joule’s Law James Joule (1818 – 1889) – showed that heat and electrical energy are interchangeable. Joule’s Law: Power = Voltage x Current P = V I Watts = Volts x Amperes

22. U3e-L2 Let’s look at problem #4, which is very similar to problem #1: 4.A cell phone charger converts the wall outlet voltage to 5 Volts to charge the cell phone. The amount of current that the charger outputs is.7 Amperes. Sketch a schematic diagram of this circuit. What is the power used by the cell phone in recharging its battery? 1)Write the given information: V = 5 volts I =.7 amps P = ? Problems – Joule’s Law A schematic is a diagram that represents the elements of a system without using realistic pictures

23. U3e-L2 1)Write the given information: V = 5 volts I =.7 amps P = ? 2)Sketch a schematic diagram of the circuit: a)Start with power source b)Add conductors c)Add resistance d)Add current Problems – Joule’s Law V = 5V I =.7A - + P = ?

24. P = V I P = 5V x.7A P = 3.5 W 1)Write the given information: V = 5 volts I =.7 amps P = ? 3)Write Formula, Substitute, and Solve Problems – Joule’s Law V = 5V I =.7A - + P = ? 2)Sketch a schematic diagram of the circuit: U3e-L2

25. Complete problem #5 on your worksheet Problems – Joule’s Law U3e-L2

26. 5.A Honda Insight (hybrid) has a 144 Volt battery system in its trunk. The electric motor that the batteries power can generate 20,000 Watts of power. Sketch a schematic diagram of this circuit. What is the current traveling through this high voltage circuit? 1)Write the given information: V = 144 volts P = 20,000 watts I = ? Problems – Joule’s Law A schematic is a diagram that represents the elements of a system without using realistic pictures

27. 1)Write the given information: V = 144 Volts P = 20,000 Watts I = ? 2)Sketch a schematic diagram of the circuit: Start with power source Add conductors Add load Add current Problems – Joule’s Law V = 144V I = ? - + P = 20,000 W U3e-L2

28. 1)Write the given information: V = 144 Volts P = 20,000 Watts I = ? 3)Rearrange, Substitute, and Solve Problems – Joule’s Law V = 5V I =.7A - + R = ? 2)Sketch a schematic diagram of the circuit: P = V x I I = 20,000W / 144V R = 138.9 A I = P / V U3e-L2

29. Complete the worksheet on electrical problems using Joule’s and Ohm’s Laws