resistance, ohm’s law, and power
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
Georg Simon OhmGeorg Simon Ohm
ResistancePotential Difference
Current
RVI
SI Unit: Ohms (Ω)
For many materials the Resistance is constant over a wide range of applied potential differences
VI
Constant
ΔV=IR
m=?
Do not follow Ohm’s Law (resistance does vary with the applied voltage)
Potential Difference (V)
Have NO resistance below a critical temperatureHave 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
• 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
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
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 kWh (energy delivered in 1 h at constant rate of 1 kW)
1KW h103W
1kW60min
hour60s
min3.6106W s3.6106J