1. Electrical Circuits ALESSANDRO VOLTA (1745-1827) GEORG SIMON OHM (1789-1854) ANDRE MARIE AMPERE (1775-1836)

2. Sources of Voltage (Energy) solar geothermal wind hydroelectric chemical piezoelectric nuclear ALLESANDRO VOLTA AND THE ELECTRIC BATTERY A VOLTAGE SOURCE IS LIKE A WATER PUMP biomass Voltage, also known as “electromotive force” can be create by many sources of energy

3. Electrical Current Current is the rate of flow of charge through a conductor. SI units CURRENTEFFECT 0.0001 Athreshold of feeling 0.001 Amild shock felt 0.005 Ashock is painful 0.015 Amuscle control is lost 0.100 Adeath can occur Current flow is defined in the direction of positive charge; since electrons flow in wires, current is opposite the flow of electrons. Small microamp (  A) currents flow through your body, but larger amounts of current are dangerous, even deadly.

4. Electrical Current Moving electrons collide with vibrating atoms, so they zigzag in a random path, with a slow forward drift velocity. Potential difference creates an electric field in a circuit. The electric field induce charge to flow. Although the electric field travels at near the speed of light, the drift velocity of electrons is less than a millimeter per second. Electrons do not race around a circuit! click for animation

5. Electrical Resistance Resistance is a measurement of a material’s ability to resist the flow of electrical charge. Resistivity depends on the nature of a material. Conductors have low resistivity and insulators have high resistivity. SI units Resistance depends on the material’s type, length, cross- section, and temperature. click for resistance codes resistance applet

6. Alternating versus Direct Current Alternating current (ac) switches the direction of the current back and forth at 60 times per second (60 Hertz). North America uses ac for its power grid because it was safer and more reliable when infrastructure began. Most devices use direct current so a transformer converts ac to dc often at lower voltage. Direct energy conversion devices like light bulbs, heaters, can run off ac or dc click for animation ALTERNATING CURRENT DIRECT CURRENT Batteries provide direct current (to increase battery life). Thomas Edison brought direct current to the masses. Nikola Tesla proved alternating current to be more efficient.

7. Electrical circuit versus a water circuit Ohm’s Law When a device shows a linear relationship between voltage and current, it is said to be “ohmic” OHMICNONOHMIC click for animation click for animation ONE-WAY (DIODE)

8. Energy, Power, and Cost in Circuits POWER LAW Combine Power Law with Resistance equation Cost of Electrical Power Example - Find the cost of a 1500 watt hair dryer run for 12 minutes, using the rate of $0.10 per kilowatt hour.

9. Kirchoff’s Rules Rule #1 - The Loop Rule Rule #2 - The Junction Rule The sum of the potential differences (voltages) around any closed loop in a circuit must be zero The current entering a junction in a circuit equals the current leaving the junction A statement of conservation of energy A statement of conservation of charge -6 v-2 v -4 v +12 v example 3 A 5 A 2 A 10 A example

10. Series Circuits A series circuit has only one pathway around the circuit Rule # 1 means that the voltage across all resistors in series must add up to the source voltage Rule # 2 means that the current through all resistors in series must equal the source current Combine the two equations: click for animation

11. Series Christmas Tree Lights Series wiring was often used for Christmas tree lights When the bulb burns out, the jumper now has 120 volts across it. One bulb burns out, they all go out! Who’s to say which one burned out! Modern bulbs use a “jumper” wire. This wire has insulation around it. The voltage produces a spark, and the insulation burns off. The circuit is now complete, with the one bulb not lit but easily replaced.

12. Parallel Circuits A parallel circuit has multiple pathways around the circuit Rule # 1 means that the voltage across all resistors in parallel must equal the source voltage Rule # 2 means that the current through all resistors in parallel must add up to the source current Combine the two equations: click for animation click for animation

13. Combination Circuits A combination circuit must be simplified into groups of series and parallel resistors, and then the equivalent for each group is then found. click for animation click for animation

14. Combination Circuits The total current in the combination circuit is determined and used to work “backwards” to find other branch currents and resistor voltages. Find current through circuit Find voltage across 3   equivalent Find current through 12   equivalentFind voltage across 2   resistor