1. Electricity Charge, Current, etc…

2. Charge When an object has the ability to attract and repel, caused by the excess or deficiency of electrons (e -). Too many e –’s: negative charge Too few e –’s: positive charge Like charges repel Opposite charges Attract + + - - - + + -

3. Charges aren’t “created” or “destroyed,” just re-arranged. The total # of electrons and protons stay constant.

4. …Side Note… The word electricity comes from the Greek word “electros” which means amber. Amber was prized as jewelry and it could be also charged electrically by friction… not only pretty – entertaining too!

5. Coulomb’s Law Charges exert forces on each other. Coulomb’s Law describes the force. Does this formula look familiar? Where… q 1 = charge #1 (in Coulombs) q 2 = charge #2 (in Coulombs) K = constant of 9x10 9 (Nm 2 /c 2 ) R = distance between charges

6. Electric Field Analogous to gravitational force vs. acceleration, take away one charge…

8. Electrostatic Induction An alternate way of charging objects other than friction… Electric Induction occurs when a charged object attracts an uncharged object. - - - - - - - - Charged rod + + + + + + + + - - - - - - - - - - - - - + + + + + + + + - - - - - - - - - - - - -

9. Electrostatics vs. Gas Stations

10. Electric Current When electric charges moves, it is called current. In 1794, Italian scientist Alessandro Giuseppe Antonion Anastasion Volta invented the first device that could sustain an electric current.

11. The first battery… The electric battery: Volta found that if two dissimilar metals are immersed in a conductive chemical solution, an electric current flows from one metal to the other. The zinc accumulates e-’s through chemical reactions with the solution. The copper loses electrons & gains a positive charge. The accumulated zinc electrons start to flow to the copper, causing a current. Although the electrons flow from negative to positive, the current flows from positive to negative. ++++++++++++++ -------------- + copper - zinc Current Flow Electron Flow

12. Battery continued The electron difference between two points is called the potential difference, or VOLTAGE. A steady flow of electrons caused by a potential difference is called a direct current, or DC. As the current flows from positive to negative charge, work is done, which is used to run motors, light lamps, heat coils, etc… The rate at which the work is produced is called electric power, which has the same units as mechanical power. We get the following formula…

13. POWER P = I x V (Power) = (Current)x(Voltage) With units: Power in Watts, Current in Amperes, Voltage in Volts Not all cell phone chargers are the same!

14. The water analogy Imagine that electric current is like water flowing through a pipe: Electricity: H 2 0 Coulomb of charge:liter H 2 0 Ampere:liter/sec Battery:pump Voltage:pump pressure Wire:pipe Resistor:pipe filled w/ rocks Pump House Clear pipe filled with rocks.

15. The water analogy… The pump house will cause the water to flow from one end to the other. The rocks will provide a necessary resistance to the water; if there was no resistance, the pump soon be overloaded. In an electrical circuit, zero resistance will overload the power supply.

16. Ohm’s Law V = I R Where R is the resistance, with the unit Ohms (Ω)

17. Why is electricity dangerous? What electrical property is responsible for bodily damage? The answer is current. Only.07 amps can kill you!! When a high current passes through the body, it can burn tissue and disrupt nerve functions (causing heart or lung failure). However, since current, voltage and resistance are all related (Ohm’s law) they are all somewhat involved in the shock.

18. High V means high current, so if you see a sign that reads “Warning - 1000 V”, the volts won’t kill you, but the current it creates will! Also, if you lower the resistance, the current goes up. If your R is low enough, even household voltage of 120 V can kill you.

19. Types of Circuits Series circuit: Current only has one pathway If one bulb burns out, the entire circuit is out Voltage differs across each light. R T = R 1 + R 2 + R 3 + …

20. Types of Circuits Parallel Circuit: Current has multiple paths If one light burns out, the rest stay lit Voltage is the same across each bulb The more paths, the less the total R To calculate total current or voltage:

21. Overloads Your house is a large parallel circuit (think of what your circuit breakers are connected to). You “blow a fuse” when too many resistors are being used from one plug (hair dryer, microwave, etc…). The more things in parallel, what happens to the total resistance? What happens to the current?

22. Electrician Questions 1. How many 100 W light bulbs can you place on a 15 A circuit? 2. On a 10 A circuit?