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Flow rate depends on: Potential difference Area (size of “pipe”) Permeability (or “roughness”). Water flows from high potential to low potential. High potential. Same high potential. Lower potential. A high flow rate generates lots of power.
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Flow rate depends on: • Potential difference • Area (size of “pipe”) • Permeability (or “roughness”)
Water flows from high potential to low potential High potential Same high potential Lower potential A high flow rate generates lots of power
In a water pipe:“Conductance” is proportional to AREA x PERMEABILITY • Area (size of “pipe”) • Permeability (if the water must flow around sand or gravel in the pipe) • The opposite of Conductance is • “RESISTANCE”
In an electric wire or light bulb:“Conductance” is proportional to AREA x CONDUCTIVIY • Area (size of “wire” or “filament”) • Conductivity (the current must flow around atoms in the wire) • The opposite of Conductance is • “RESISTANCE”
Units: • “Fluid potential” is measured in the same units as “pressure” • The SI unit of pressure is the Pascal or “Pa” • Pascals are tiny so we often usekilopascals or “kPa”
Units: • A useful unit for work and energyis the joule. • One joule is about ¼ calorie. • One joule is also the energy neededto move one literof water through apotential difference of one kPa.
Units: • Power is “energy per unit time” • Power is measured in watts • 1 watt = 1 joule per second
Units: • 1 watt = 1 joule per second • Lighting a 40 watt bulb for 10 seconds consumes 400 joulesof energy • 1 kWhr = (1 kW)(3600 s) = 3.6 million joules
Electrical Units: • The stuff that flows is called CHARGE • The unit of charge is the COULOMB • The flow of charge is called CURRENT • The unit of current is the AMP
Electrical Units: • The unit of potential is the VOLT • A potential difference is called VOLTAGE
Electrical Units: • The unit of energy is the JOULE • Energy is determined by • The amount of charge that moves • The change in potential of each charge
Electrical Units: • The unit of power is the WATT • Power is determined by • The rate of motion of charge (CURRENT) • The change in potential of each charge