Transcript The water cycle and energy transformations

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)