1. The study of electric charges in motion Electric Current

2. Potential Difference (V) Charge flows from higher potential to lower potential until electric potential equilibrium is reached. When electric potential is zero (equilibrium), current flow stops.

3. Example: Charge Distribution What is the total charge of three conducting spheres with charges of 6q,-1q, and 0q A 6q B -1q C 0q

4. Example: Charge Distribution cont. What is the final charge distribution if sphere A and B touch? C 0q A 6q B -1q B 2.5q A 2.5q

5. Example: Charge Distribution cont. What is the final charge distribution if sphere B and C touch? B 2.5q A 2.5q C 0q C 1.25q B 1.25q

6. Example: Charge Distribution cont. What is the total charge of three conducting spheres A 2.5q C 1.25q B 1.25q

7. Electric Current Electrical charge in motion is electric current. Current is measured by counting the amount of charges that pass a given point per second SymbolvariableUnit IcurrentA (amp)

8. Comparing a DC circuit to Flow of Water http://faraday.physics.utoronto.ca/IYearLab/Intros/DCI/Flash/WaterAnalogy.html What component in the electrical circuit is equivalent to the pump in the animation?

9. Direct Current (DC) DC stands for direct current. Here current only travels in one direction.

10. Alternating Current (AC) AC stands for alternating current. Here current switches directions at a set frequency.

11. Alternating Current (AC)

12. Voltage Current flows only when there is a potential difference (V) Voltage sources can sustain a potential difference Voltage in a circuit is analogous to pressure in a water hose. Voltage Source OFFON

13. Voltage Sources There are different types of devices that can provide a source of voltage. Sources that provide DC include: –Batteries –DC Power Supplies –DC Generators Sources that provide AC include: –Electrical Outlets –Alternators –Power Inverters

14. Electric Circuits Electric current flows very well if there is a complete loop for charge to flow. This is called an electrical circuit. Circuits often contain various elements, giving it practical use. Examples of circuit elements include: –Switches –Sources of Resistance (Such as a Light) –Meters

15. Circuit Symbols Each circuit element has its own symbol. Common circuit symbols are shown below. Resistor Switch WireBattery Voltmeter Ammeter A Conductor of Current Opens and Closes Circuits Provides Resistance to Current Flow Source of DC Charge Flow Measures Current Measures Voltage

16. More Circuit Symbols Here are some additional circuit symbols that you may see. Potentiometer AC Source Ground Crossing Junction Capacitor Diode Stores Charge on Plates Variable Resistor Provides AC Current Drains Excess Charge Buildup Only Allows Current to Flow One Way All Four Wires Connect Wires Only Cross and do not Connect.

17. Electrical Resistance Every circuit contains some resistance to current flow. This is due to imperfections in the crystalline lattice structure of the conductor. Imagine the lattice structure below is the atoms in a wire. Notice how the moving electrons experience resistance. The variable for resistance is R. The unit for resistance is the Ohm (symbol  ).

18. Ohm’s Law The current in a circuit is directly proportional to voltage and inversely proportional to resistance. This relationship is known as Ohm’s Law. Resistance (  ) Voltage (V) Current (A)

19. Sample Problem (Ohm’s Law) A toaster is connected to a 120V outlet and draws 3A of electrical current. What is the resistance of the toaster?

20. Power (Watt W) Power measures the rate at which energy is transferred. Thermal energy P=I 2 R –Wasted or unwanted energy during transmission

21. Power and Electricity There are also two useful equations that relate power to electrical quantities. Notice how current is squared in the second equation. Increasing current in a circuit drastically increases the power consumed. High current wires generate heat. This is why electricity transferred over large distances is at high voltage and not high current. Otherwise, the power losses would be very wasteful.

22. Resistance of power lines is.2 ohms per Km How much power is lost during transmission if a home 3.5Km from the power plant cooks on a stove that draws 41A?

23. How can energy loss be reduced? Either reduce I or R R is a fix physical property

24. High voltage lines transmit power between 500,000V- 750,000V to reduce energy loss.

25. Sample Problem (Electrical Power) What is the power consumed when the toaster in on for 45s ? Given

26. The Kilowatt Hour Did you ever read an electric bill? You are charged for the number of kilowatt hours used during the month. This is energy, not power, because: The amount of kilowatt-hours gets multiplied times a rate to find the overall energy cost. Power (kW) Time (h) Cost ($) Rate Energy (kWh) 1kW =1000W

27. How Much Energy is a kWh? We all know that the SI unit for energy is the Joule (J). How many Joules are there in one kilowatt hour? or

28. Sample Problem (KWh) During the winter, an electric heater runs 8 hours every day over the course of a month (30 days). The power consumed by the heater is 1200W. How many kWh of energy are consumed? If the rate is $0.11 per kWh, then what is the cost to operate the heater?

30. Example: Charge Distribution cont. Sphere B is twice as large as sphere A, what will be the charge distribution after they touch? A 5q B 5q A 3.33q B 6.67q

31. Electric Circuit & Energy Conversion Video Clip

32. Electron flow & Current video clip