Current Electricity

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  • *but instead of water flowing through the interior of a pipe, electricity is a flow of electrons across the surface of a metal (or other conductive material)
  • Like water, voltage (electrical force through potential difference) has the ability to do more work (or damage) with greater flow. (Wind causing a wave vs. earthquake causing a tsunami) If VOLTAGE is the FORCE pushing the water/electricity, CURRENT is how MUCH is flowing past per second
  • Lithium cobalt oxide and carbon (Li ion battery) manganese dioxide and zinc (Alkaline battery) lead dioxide and metallic lead (Car battery)
  • Zinc-carbon battery : The zinc-carbon chemistry is common in many inexpensive AAA, AA, C and D dry cell batteries. The anode is zinc , the cathode is manganese dioxide, and the electrolyte is ammonium chloride or zinc chloride. Alkaline battery : This chemistry is also common in AA, C and D dry cell batteries. The cathode is composed of a manganese dioxide mixture, while the anode is a zinc powder. It gets its name from the potassium hydroxide electrolyte, which is an alkaline substance. Lithium-ion battery (rechargeable) : Lithium chemistry is often used in high-performance devices, such as cell phones, digital cameras and even electric cars. A variety of substances are used in lithium batteries, but a common combination is a lithium cobalt oxide cathode and a carbon anode. Lead-acid battery (rechargeable) : This is the chemistry used in a typical car battery. The electrodes are usually made of lead dioxide and metallic lead, while the electrolyte is a sulfuric acid solution.
  • Current Electricity

    1. 1. Current Electricity
    2. 2. Electricity <ul><li>Electricity is: </li></ul><ul><ul><li>the movement of charged particles from one place to another. </li></ul></ul>
    3. 3. Static vs. Current <ul><li>How is static electricity different than current electricity? </li></ul><ul><ul><li>Static electricity involves a build-up of electric charge with a singular, momentary discharge. </li></ul></ul><ul><ul><li>Current electricity pertains to a continuous flow of electricity through a conductor. </li></ul></ul><ul><li>Name two examples of each. </li></ul><ul><ul><li>Static : lightning, static shock </li></ul></ul><ul><ul><li>Current : wall outlet, battery </li></ul></ul>
    4. 4. Current Electricity <ul><li>A constant flow of charged particles through a conductive medium </li></ul><ul><li>Measured in Amperes (A) </li></ul><ul><ul><li>1 Amp = 6 billion billion electrons per second moving past a point </li></ul></ul>
    5. 5. Circuits <ul><li>An electric circuit is a closed path of conductors through which current can flow </li></ul><ul><ul><li>similar to water flowing through a pipe </li></ul></ul>
    6. 6. Current Flow <ul><li>Electrons need some incentive to get started in order for electricity to flow. </li></ul><ul><ul><li>A difference in electrical potential (build-up of charges) provides the force required for current to flow </li></ul></ul><ul><li>Potential Difference: a measure of the difference in charges (electric PE) between two points </li></ul><ul><ul><li>also called Electro-Motive Force (EMF) or Voltage </li></ul></ul><ul><ul><li>this force causes work to be done (current to flow) </li></ul></ul><ul><ul><li>measured in Volts </li></ul></ul>
    7. 7. Voltage <ul><li>Voltage is the force created by a difference in electrical potential </li></ul><ul><ul><li>similar to water pressure </li></ul></ul><ul><li>Voltage examples: </li></ul><ul><ul><li>AA battery: 1.5 V </li></ul></ul><ul><ul><li>9 Volt battery: 9 V </li></ul></ul><ul><ul><li>Car battery: 12 V </li></ul></ul><ul><ul><li>Household outlet: 120 V </li></ul></ul><ul><ul><li>Electric chair: 1000 - 2450 V </li></ul></ul>
    8. 8. Batteries <ul><li>Cells are individual compartments in a battery that produce energy </li></ul><ul><li>Chemical reactions take place which produce electricity </li></ul><ul><ul><li>two electrodes (electron conductors) </li></ul></ul><ul><ul><ul><li>each electrode is made of a different material </li></ul></ul></ul><ul><ul><li>electrolyte liquid or paste </li></ul></ul><ul><ul><ul><li>allows ions to flow between </li></ul></ul></ul>
    9. 9. Inside Batteries <ul><li>Electrodes: </li></ul><ul><ul><li>one material donates electrons </li></ul></ul><ul><ul><ul><li>negative electrode (anode) </li></ul></ul></ul><ul><ul><ul><li>connects to - terminal (outside) </li></ul></ul></ul><ul><ul><li>other material accepts electrons </li></ul></ul><ul><ul><ul><li>positive electrode (cathode) </li></ul></ul></ul><ul><ul><ul><li>connects to + terminal </li></ul></ul></ul><ul><li>Electrolyte: </li></ul><ul><ul><li>paste in dry cell </li></ul></ul><ul><ul><ul><li>i.e. alkaline (basic pH) </li></ul></ul></ul><ul><ul><li>liquid in wet cell </li></ul></ul><ul><ul><ul><li>i.e. sulfuric acid </li></ul></ul></ul>Dry Cell Wet Cell
    10. 10. Resistance <ul><li>Resistance is the tendency of a material to oppose current </li></ul><ul><ul><li>measured in Ohms ( Ω ) </li></ul></ul><ul><ul><li>conductive materials have lower resistance </li></ul></ul><ul><ul><li>increased resistance can produce heat & light </li></ul></ul><ul><ul><ul><li>i.e. tungsten filaments in light bulbs </li></ul></ul></ul><ul><li>Resistors in electronics control the flow of electricity </li></ul>
    11. 11. Resistance <ul><li>Resistance affects voltage (force) and current (amount) of electricity flow </li></ul><ul><ul><li>Resistance is affected by: </li></ul></ul><ul><ul><ul><li>conductivity of the material </li></ul></ul></ul><ul><ul><ul><li>length of wire (longer wire = more resistance) </li></ul></ul></ul><ul><ul><ul><li>diameter of wire (wider wire = less resistance) </li></ul></ul></ul><ul><ul><ul><li>temperature </li></ul></ul></ul><ul><ul><ul><ul><li>in metals </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>higher temps = more resistance </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><li>in carbon/silicon </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>higher temps = less resistance </li></ul></ul></ul></ul></ul>
    12. 12. Ohm's Law <ul><li>Voltage = Current x Resistance </li></ul><ul><ul><li>(V) volts (I) amps (R) ohms </li></ul></ul><ul><li>V = I • R </li></ul><ul><li>Current = Voltage  Resistance </li></ul><ul><li>I = V/R </li></ul><ul><li>Resistance = Voltage  Current </li></ul><ul><li>R = V/I </li></ul>Georg Simon Ohm (1787 - 1854)
    13. 13. Ohm's Law <ul><li>if I (current) = .005 amps </li></ul><ul><li>and V (voltage) = 10 volts </li></ul><ul><li> what is the resistance ( R )? </li></ul><ul><li>What formula should we use? </li></ul><ul><li>R = 10V/.005A </li></ul><ul><li>Resistance = 2,000 Ω </li></ul>R = V/I
    14. 14. DC & AC <ul><li>Direct Current (DC): electrons flow in one direction only </li></ul><ul><ul><li>current flows from negative to positive </li></ul></ul><ul><ul><li>example: batteries </li></ul></ul><ul><li>Alternating Current (AC): the direction of current changes rapidly over time </li></ul><ul><ul><li>electrons change direction (move back and forth along a conductor) 60 times every second </li></ul></ul><ul><ul><li>positive & negative terminals constantly change </li></ul></ul><ul><ul><li>example: household wiring </li></ul></ul>

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