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Resistance, Ohm’s Law, and Power

Resistance, Ohm’s Law, and Power. Georg Simon Ohm. Resistance:. The impedance of the motion of charge through a conductor. SI Unit: Ohms (Ω). Ohm’s Law:. For many materials the Resistance is constant over a wide range of applied potential differences. m= ?. ΔV=IR.

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Resistance, Ohm’s Law, and Power

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  1. Resistance, Ohm’s Law, and Power Georg Simon Ohm

  2. Resistance: • The impedance of the motion of charge through a conductor SI Unit: Ohms (Ω)

  3. Ohm’s Law: • For many materials the Resistance is constant over a wide range of applied potential differences m=? ΔV=IR

  4. Factors that Affect Resistance:

  5. Non-Ohmic Materials • Do not follow Ohm’s Law (resistance does vary with the applied voltage) Current (I) Potential Difference (V)

  6. Superconductors!!! Have NO resistance below a critical temperature Good Superconductors: *Zn, Al, Sn, Hg, Nb, Nb3Ge, YBa2Cu3O7, TI-Ba-Ca-Cu-O *Cu, Ag, and Au are not Superconductors

  7. Applications • Resistors in a circuit can change the current. • Variable resistors (potentiometers) are used in dimmer switches and volume controls. • Resistors on circuit boards control the current to components. • The human body’s resistance ranges from 500 000  (dry) to 100  (soaked with salt water). • Currents under 0.01 A cause tingling. • Currents greater than 0.15 A disrupt the heart’s electrical activity

  8. Electric Power: • P=W/t… (rate at which work is done) • Electric power: rate at which charge carriers convert electrical potential to nonelectrical forms of energy (ΔPE/t…conversion in book) P = IΔV = I(IR) = I2R P = IΔV = (ΔV/R)ΔV = (ΔV)2/R

  9. SI Unit for Power: Watt 1W= 1J/s • (1 joule of energy being converted into another form per second) • Electric Companies charge for energy, not power. Electricity is measured in terms of kWh (energy delivered in 1 h at constant rate of 1 kW)

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