1. Ohm’s Law

2. From Static to Electric current  You cannot rub a balloon on your head and then plug in your radio to run off the charge on your hair…darn!!!!  Electric current is the flow of electric charge through a conductor either in one direction (DC) or alternating directions (AC).

3. Pushing charge along  Just as water will not flow in a pipe unless one end is at a different gravitational potential than the other, electric charge will not “flow” unless there is a difference in Electric potential across a conducting path.  Electric potential= electrical potential energy / charge.  1volt = 1 joule / 1 Coulomb  A coulomb is the unit of charge.

4. How do you flow?  In order to keep charge moving, there must continue to be a difference in electric potential.  Several sources provide this difference: Generator (produces AC) Battery (produces DC) Photovoltaic cell (solar cell)  Voltage provides the electric pressure that moves the charges. Voltage may also be called electromotive force (emf).

5. Electric Current  Recall Static Electricity is a buildup of charge.  Electric charge that flows from one place to another (sustainable) is called electric current.  Conventional current is the flow of “positive” charge from high potential difference to low potential difference.  The unit of current is the ampere or amp (A). One amp means one coulomb of charge flows per second.

6. Effects of Various Electric Current on the Body Current in AmpsEffect 0.001 ACan be felt (tingle) 0.005 APainful 0.010 AMuscle Spasms 0.015 ALoss of Muscle Control 0.070 AFatal if longer than 1 sec

7. Obstacles  The flow of electric current can be interrupted by the object it passes through.  Resistors dissipate energy by heat. The material of the resistor is conductive, but not as conductive as the wire used to connect circuit components. The symbol for a resistor is:  This is called resistance. Resistance is measured in ohms (  ). High resistance harder for charge to pass through. Low resistance easier for charge to pass through. 15 

8. Factors affecting resistance  Resistance of an object depends on the material it is made of. Copper is a better conductor than iron.  If your skin gets wet, your resistance is lower and the currents can rise to dangerous levels of tens of milliamps.  (Lie detector test?)  Length of a wire affects resistance as well as diameter.

9. Look inside a Resistor

10. Resistor in a Circuit i

11. Resistance and Ohm’s Law  Any device that uses current or controls how much current will flow is called a resistor.  Resistance is the ratio of potential difference, V, to current, I.  Resistance is measured in Ohms, Ω. V RI

12. Power  A charge moving in a circuit expends energy.  This might result in heating the circuit, or turning a motor.  The rate at which electrical energy is converted to another form, such as mechanical, heat or light, is called Electric Power.

13. Current and Power  The rate of charge flow is called current, I, and is measured in coulombs / sec or amperes, A.  Power is the rate energy is transferred.  1J/1s = 1 watt  Power = I * V  (3.0 C/s) * (120 J/C) = 360 W

14. AA 6 volt battery delivers 0.5 A of current to an electric motor connected across its terminals. What is the power of the motor? A. 3 w B. 12 w C. 5.5 w D. 6.5 w Example

15. Electricity

16. Capacitors  Capacitors store energy as an electric field bound between the plates of the capacitor. The charge polarity of the capacitor will match the polarity of the circuit power source. Once a capacitor is charged, no additional current will flow through. The symbol for a capacitor is: 50 F

17. E Capacitor in a Circuit E E E

18. Electric Circuits  When charge flows through a conductor in a continuous loop from a voltage source (pump) and back to it, we have an electric circuit.  The total amount of charge in the circuit does not change as it moves around.  Electric energy can then be converted to different forms like light, thermal energy, mechanical energy, etc…

19. Drawing Circuit Diagrams  Light up a bulb with one wire and one battery.  Draw 4 DIFFERENT ways this can happen.  Next let’s draw your “circuit” in schematic terms.

20. Electric Circuit Symbols

21. Your turn to Practice  Homework: Pg. 526 #’s 3, 4, 9, 11-13, 21, 27, 33, 38, 47