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Electricity: Current, Voltage, Conductors & Insulators

Learn about the fundamentals of electricity, including conductors, insulators, current, and voltage. Explore topics such as Ohm’s Law, electric potential, and sources of electric potential. Enhance your knowledge of electrical concepts.

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Electricity: Current, Voltage, Conductors & Insulators

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  1. Electricity--- Current and voltage

  2. Summary of conductors and insulators • Conductors – need free (mobile) charges In metals there are free electrons • Insulators have all charges firmly bound (glass, most plastics) • air? • Human body? Faraday’s Cage

  3. Electric current

  4. Q0 The electric current in this case, • increases • decreases • remains unchanged as a function of time.

  5. Voltage Before plates are connected, certain electric energy is stored. These energy stored is characterized electric potential difference or Voltage.

  6. conduction electrons in a wire No connected to charged plates When connected to plates

  7. Maintain a constant electric current

  8. A Battery keeps current flowing !! Voltage of a battery

  9. Electric potential Gravitational Potential Energy mgh Gravitational Potential gh Electrical potential Energy qV Electrical potential V

  10. Some Typical Voltages Voltage Source (approx.) Thundercloud to ground 108 V High-voltage power line 106 V Power supply for TV tube 104 V Automobile ignition 104 V Household outlet 120 V Automobile battery 12 V Flashlight battery 1.5 V Resting potential across nerve membrane 10-1 V Potential changes on skin (EKG and EEG) 10-4 V

  11. Sources of electric potential • Batteries • Van de Graaff generator • Power stations • Alternators • Wind generators • Solar panels • Piezoelectric materials

  12. Electric current The bigger the voltage, The bigger the current.

  13. Current: the flow of charges. • I = Q/t • SI Unit ampere A • What kind of charges? electrons, ions, holes

  14. Q1 A and B copper wires of same lengths connected to two identical batteries. A with bigger cross-section than the other. A should carry a • Bigger current; • Smaller current; • Same current; • None of above .

  15. Q2 A and B copper wires of same cross sections. A is longer than B. A should carry a • Bigger current; • Smaller current; • Same current; • None of above.

  16. Ohm’s Law I = σA V/d = V / R where A is a cross section area of a wire, d is length. V is the voltage across the wire. We call the quantity characterizing the material conductivity σ. Inverse of σ is called resistivity ρ, ρ = 1/σ R= ρ d/A

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