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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” Imagine water flowing in a “loop” or “circuit” Imagine water flowing in a “loop” or “circuit” Imagine water flowing in a “loop” or “circuit” Imagine water flowing in a “loop” or “circuit” 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 use kilopascals or “kPa” Units: • A useful unit for work and energy is the joule. • One joule is about ¼ calorie. • One joule is also the energy needed to move one liter of water through a potential 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 joules of 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 1 𝑐𝑜𝑢𝑙𝑜𝑚𝑏 1 𝑎𝑚𝑝 = 𝑠𝑒𝑐𝑜𝑛𝑑 Electrical Units: • The unit of potential is the VOLT • A potential difference is called VOLTAGE 1 𝑗𝑜𝑢𝑙𝑒 1 𝑣𝑜𝑙𝑡 = 𝑐𝑜𝑢𝑙𝑜𝑚𝑏 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 𝐸𝑛𝑒𝑟𝑔𝑦 𝑖𝑛 𝑗𝑜𝑢𝑙𝑒𝑠 = (𝑐ℎ𝑎𝑟𝑔𝑒)(𝑣𝑜𝑙𝑡𝑎𝑔𝑒) 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 𝑃𝑜𝑤𝑒𝑟 = (𝑐𝑢𝑟𝑟𝑒𝑛𝑡)(𝑣𝑜𝑙𝑡𝑎𝑔𝑒) 𝑤𝑎𝑡𝑡𝑠 = (𝑎𝑚𝑝𝑠)(𝑗𝑜𝑢𝑙𝑒𝑠)