The water analogy seems to imply that power = current. Why is this incorrect?











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Many people think of the water analogy to try to explain how electromagnetic energy is delivered to a device in a circuit. Using that analogy, in a DC circuit, one could imagine the device is like a water wheel being pushed by the current.



In the case of an actual water wheel, the more water that flows per unit of time, the more energy gets delivered to the wheel per unit of time: power = current, but in electric circuits power = voltage x current.



Why is this?










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  • Can you make your post a little more exact? Are you saying Power = Current? Please define all terms. And make sure units match up.
    – ggcg
    4 hours ago










  • Thanks. Is it more clear now?
    – lyndon
    4 hours ago










  • en.wikipedia.org/wiki/Hydraulic_analogy#Equation_examples
    – BowlOfRed
    3 hours ago










  • In the case of a water wheel, it's the amount of water flowing times how hard the water pushes the wheel.
    – immibis
    2 mins ago















up vote
1
down vote

favorite












Many people think of the water analogy to try to explain how electromagnetic energy is delivered to a device in a circuit. Using that analogy, in a DC circuit, one could imagine the device is like a water wheel being pushed by the current.



In the case of an actual water wheel, the more water that flows per unit of time, the more energy gets delivered to the wheel per unit of time: power = current, but in electric circuits power = voltage x current.



Why is this?










share|cite|improve this question
























  • Can you make your post a little more exact? Are you saying Power = Current? Please define all terms. And make sure units match up.
    – ggcg
    4 hours ago










  • Thanks. Is it more clear now?
    – lyndon
    4 hours ago










  • en.wikipedia.org/wiki/Hydraulic_analogy#Equation_examples
    – BowlOfRed
    3 hours ago










  • In the case of a water wheel, it's the amount of water flowing times how hard the water pushes the wheel.
    – immibis
    2 mins ago













up vote
1
down vote

favorite









up vote
1
down vote

favorite











Many people think of the water analogy to try to explain how electromagnetic energy is delivered to a device in a circuit. Using that analogy, in a DC circuit, one could imagine the device is like a water wheel being pushed by the current.



In the case of an actual water wheel, the more water that flows per unit of time, the more energy gets delivered to the wheel per unit of time: power = current, but in electric circuits power = voltage x current.



Why is this?










share|cite|improve this question















Many people think of the water analogy to try to explain how electromagnetic energy is delivered to a device in a circuit. Using that analogy, in a DC circuit, one could imagine the device is like a water wheel being pushed by the current.



In the case of an actual water wheel, the more water that flows per unit of time, the more energy gets delivered to the wheel per unit of time: power = current, but in electric circuits power = voltage x current.



Why is this?







fluid-dynamics electric-circuits electric-current power flow






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share|cite|improve this question













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edited 3 hours ago









Qmechanic

101k121821135




101k121821135










asked 4 hours ago









lyndon

303




303












  • Can you make your post a little more exact? Are you saying Power = Current? Please define all terms. And make sure units match up.
    – ggcg
    4 hours ago










  • Thanks. Is it more clear now?
    – lyndon
    4 hours ago










  • en.wikipedia.org/wiki/Hydraulic_analogy#Equation_examples
    – BowlOfRed
    3 hours ago










  • In the case of a water wheel, it's the amount of water flowing times how hard the water pushes the wheel.
    – immibis
    2 mins ago


















  • Can you make your post a little more exact? Are you saying Power = Current? Please define all terms. And make sure units match up.
    – ggcg
    4 hours ago










  • Thanks. Is it more clear now?
    – lyndon
    4 hours ago










  • en.wikipedia.org/wiki/Hydraulic_analogy#Equation_examples
    – BowlOfRed
    3 hours ago










  • In the case of a water wheel, it's the amount of water flowing times how hard the water pushes the wheel.
    – immibis
    2 mins ago
















Can you make your post a little more exact? Are you saying Power = Current? Please define all terms. And make sure units match up.
– ggcg
4 hours ago




Can you make your post a little more exact? Are you saying Power = Current? Please define all terms. And make sure units match up.
– ggcg
4 hours ago












Thanks. Is it more clear now?
– lyndon
4 hours ago




Thanks. Is it more clear now?
– lyndon
4 hours ago












en.wikipedia.org/wiki/Hydraulic_analogy#Equation_examples
– BowlOfRed
3 hours ago




en.wikipedia.org/wiki/Hydraulic_analogy#Equation_examples
– BowlOfRed
3 hours ago












In the case of a water wheel, it's the amount of water flowing times how hard the water pushes the wheel.
– immibis
2 mins ago




In the case of a water wheel, it's the amount of water flowing times how hard the water pushes the wheel.
– immibis
2 mins ago










7 Answers
7






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up vote
2
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In your water example power cannot be equal to current because they have different units (power is an energy per unit time, while current would be something like a number of particles passing through a surface per unit time).




...the more water that flows per unit of time, the more energy gets delivered to the wheel per unit of time




What you have noticed here through your analogy is that power is proportional to current (as an example, the more force you apply to an object, the larger its acceleration, but this does not mean that force and acceleration are equal). In a circuit element this proportionality is the voltage, since it tells you how much energy is associated with a "unit of current". You would need a similar way to convert your water current to the power generated by that current (although this might be a simplistic model of how power is generated using a water wheel).



You also have to keep in mind that it is an analogy, and all analogies have imperfections. With the water analogy, power is generated by water actually pushing on a wheel. In circuits, $P=IV$ is much more general and applies to any charges undergoing a potential difference.






share|cite|improve this answer






























    up vote
    1
    down vote













    Here is a simple way to keep this stuff straight.



    Power is always the product of an effort variable and a flow variable. In hydraulic systems, the effort variable is pressure and the flow variable is the flow rate.



    For flow in open channels, the effort variable is typically very small (but not zero) and the flow variable is very large. BTW power exchange which occurs at low effort and large flow represents the low-impedance regime.






    share|cite|improve this answer




























      up vote
      0
      down vote













      Power is defined as work done per unit time. So a mass of water moving from one potential to some other lower potetial can do work when it hits the wheel. How much work per unit time? It depends how much mass falls times height times gravitational constant g and all of that divided by time. Water current, on the other hand is just total volume or mass that flows per unit time. Sure, it is connected to the work done or power but is not the same thing. If you define gravitational potential difference as gH and water flow as dm/dt then to have power you have to have curent times this potential difference: gHdm/dt...
      In a conductor, work is done also and energy per unit charge or potential difference is given by U (voltage) and current by dQ/dt so it seems to me that everything is same...






      share|cite|improve this answer




























        up vote
        0
        down vote













        Water and current flow as well as other “mechanical” analogies (pipe resistance vs. electrical resistance, voltage vs. pressure, etc.) are useful for introducing electrical circuit concepts at an elementary level. This is because mechanical concepts are easier to visualize whereas electrical concepts are more abstract. The analogies can only go so far without a deeper understanding.



        Current does not equal electrical power and neither does water flow equal mechanical power.



        Electrical current ($frac {Coul}{s}$) times (in phase) voltage ($frac {J}{Coul}$) equals power ($frac {J}{s}$ = watts).



        Current flow ($frac {ft^3}{s}$) times pressure ($frac {lb-f}{ft^2}$) equals power ($frac {ft-lb}{s}$). ($frac {550 ft-lb}{s}=1 hp = 746 watts$)



        The water pressure for the water wheel can come from water dropping from a height above the wheel (potential energy) or even from a hose directed horizontally, depending on the orientation of the water wheel.



        To complete the analogy between current and water flow with respect to electrical an mechanical power, you need in addition the analogy between voltage (electrical potential) and pressure (mechanical potential).



        Hope this helps.






        share|cite|improve this answer




























          up vote
          0
          down vote













          The analogy with water actually holds really nicely if you consider a water wheel, or other hydroelectric system.



          But what you're missing is that the power produced does not only depend on the amount of water going past - it also depends on the speed at which it does so. (this makes sense for the hydro system because kinetic energy depends on velocity and mass)



          To make the analogy better, rather than thinking of the speed of the flow, think about how far it has fallen to aquire that speed. At this point you have a volume per second of water - the current - and you have a loss of height, which is literally a potential difference.






          share|cite|improve this answer




























            up vote
            0
            down vote













            Power to a water-wheel depends both on the current (amount of water delivered)
            and the head (vertical drop of water as it turns the wheel). So, the
            water analogy does have TWO variables that multiply together to make
            power: current, measuring (for instance) the water flow at Niagara,
            and vertical drop (like the height of Niagara Falls).



            Current is NOT the same as power, in a river, because long stretches of
            moving water in a channel don't dissipate energy as much as a waterfall does.
            Siting a hydroelectric power plant at Niagara Falls makes sense.
            In the analogy to electricity, a wire can deliver current at little voltage
            drop (and has tiny power dissipation) but a resistor which has that same
            current will be warmed (it has a substantial terminal-to-terminal voltage drop).






            share|cite|improve this answer




























              up vote
              0
              down vote













              I'd like to put what others said already into equations:



              A river has mass flow rate $dot m$ (kg/s) (the "current"). The water flows with velocity $v$ (m/s). Power is the kinetic energy that is carried per unit time:



              $$
              dot W = frac{dot m v^2}{2}
              $$

              and notice that this has proper units of watt. If we take "voltage" to be $v^2/2$, then we get
              $$
              text{(power)} = text{(current)}timestext{(voltage)}
              $$



              Notice that the mass flow rate is not enough to give you high power. When the river is wide the velocity is low. If you want the water wheel to run fast you should build it at a narrow passage.






              share|cite|improve this answer





















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                7 Answers
                7






                active

                oldest

                votes








                7 Answers
                7






                active

                oldest

                votes









                active

                oldest

                votes






                active

                oldest

                votes








                up vote
                2
                down vote













                In your water example power cannot be equal to current because they have different units (power is an energy per unit time, while current would be something like a number of particles passing through a surface per unit time).




                ...the more water that flows per unit of time, the more energy gets delivered to the wheel per unit of time




                What you have noticed here through your analogy is that power is proportional to current (as an example, the more force you apply to an object, the larger its acceleration, but this does not mean that force and acceleration are equal). In a circuit element this proportionality is the voltage, since it tells you how much energy is associated with a "unit of current". You would need a similar way to convert your water current to the power generated by that current (although this might be a simplistic model of how power is generated using a water wheel).



                You also have to keep in mind that it is an analogy, and all analogies have imperfections. With the water analogy, power is generated by water actually pushing on a wheel. In circuits, $P=IV$ is much more general and applies to any charges undergoing a potential difference.






                share|cite|improve this answer



























                  up vote
                  2
                  down vote













                  In your water example power cannot be equal to current because they have different units (power is an energy per unit time, while current would be something like a number of particles passing through a surface per unit time).




                  ...the more water that flows per unit of time, the more energy gets delivered to the wheel per unit of time




                  What you have noticed here through your analogy is that power is proportional to current (as an example, the more force you apply to an object, the larger its acceleration, but this does not mean that force and acceleration are equal). In a circuit element this proportionality is the voltage, since it tells you how much energy is associated with a "unit of current". You would need a similar way to convert your water current to the power generated by that current (although this might be a simplistic model of how power is generated using a water wheel).



                  You also have to keep in mind that it is an analogy, and all analogies have imperfections. With the water analogy, power is generated by water actually pushing on a wheel. In circuits, $P=IV$ is much more general and applies to any charges undergoing a potential difference.






                  share|cite|improve this answer

























                    up vote
                    2
                    down vote










                    up vote
                    2
                    down vote









                    In your water example power cannot be equal to current because they have different units (power is an energy per unit time, while current would be something like a number of particles passing through a surface per unit time).




                    ...the more water that flows per unit of time, the more energy gets delivered to the wheel per unit of time




                    What you have noticed here through your analogy is that power is proportional to current (as an example, the more force you apply to an object, the larger its acceleration, but this does not mean that force and acceleration are equal). In a circuit element this proportionality is the voltage, since it tells you how much energy is associated with a "unit of current". You would need a similar way to convert your water current to the power generated by that current (although this might be a simplistic model of how power is generated using a water wheel).



                    You also have to keep in mind that it is an analogy, and all analogies have imperfections. With the water analogy, power is generated by water actually pushing on a wheel. In circuits, $P=IV$ is much more general and applies to any charges undergoing a potential difference.






                    share|cite|improve this answer














                    In your water example power cannot be equal to current because they have different units (power is an energy per unit time, while current would be something like a number of particles passing through a surface per unit time).




                    ...the more water that flows per unit of time, the more energy gets delivered to the wheel per unit of time




                    What you have noticed here through your analogy is that power is proportional to current (as an example, the more force you apply to an object, the larger its acceleration, but this does not mean that force and acceleration are equal). In a circuit element this proportionality is the voltage, since it tells you how much energy is associated with a "unit of current". You would need a similar way to convert your water current to the power generated by that current (although this might be a simplistic model of how power is generated using a water wheel).



                    You also have to keep in mind that it is an analogy, and all analogies have imperfections. With the water analogy, power is generated by water actually pushing on a wheel. In circuits, $P=IV$ is much more general and applies to any charges undergoing a potential difference.







                    share|cite|improve this answer














                    share|cite|improve this answer



                    share|cite|improve this answer








                    edited 3 hours ago

























                    answered 3 hours ago









                    Aaron Stevens

                    8,09431235




                    8,09431235






















                        up vote
                        1
                        down vote













                        Here is a simple way to keep this stuff straight.



                        Power is always the product of an effort variable and a flow variable. In hydraulic systems, the effort variable is pressure and the flow variable is the flow rate.



                        For flow in open channels, the effort variable is typically very small (but not zero) and the flow variable is very large. BTW power exchange which occurs at low effort and large flow represents the low-impedance regime.






                        share|cite|improve this answer

























                          up vote
                          1
                          down vote













                          Here is a simple way to keep this stuff straight.



                          Power is always the product of an effort variable and a flow variable. In hydraulic systems, the effort variable is pressure and the flow variable is the flow rate.



                          For flow in open channels, the effort variable is typically very small (but not zero) and the flow variable is very large. BTW power exchange which occurs at low effort and large flow represents the low-impedance regime.






                          share|cite|improve this answer























                            up vote
                            1
                            down vote










                            up vote
                            1
                            down vote









                            Here is a simple way to keep this stuff straight.



                            Power is always the product of an effort variable and a flow variable. In hydraulic systems, the effort variable is pressure and the flow variable is the flow rate.



                            For flow in open channels, the effort variable is typically very small (but not zero) and the flow variable is very large. BTW power exchange which occurs at low effort and large flow represents the low-impedance regime.






                            share|cite|improve this answer












                            Here is a simple way to keep this stuff straight.



                            Power is always the product of an effort variable and a flow variable. In hydraulic systems, the effort variable is pressure and the flow variable is the flow rate.



                            For flow in open channels, the effort variable is typically very small (but not zero) and the flow variable is very large. BTW power exchange which occurs at low effort and large flow represents the low-impedance regime.







                            share|cite|improve this answer












                            share|cite|improve this answer



                            share|cite|improve this answer










                            answered 1 hour ago









                            niels nielsen

                            14.9k42648




                            14.9k42648






















                                up vote
                                0
                                down vote













                                Power is defined as work done per unit time. So a mass of water moving from one potential to some other lower potetial can do work when it hits the wheel. How much work per unit time? It depends how much mass falls times height times gravitational constant g and all of that divided by time. Water current, on the other hand is just total volume or mass that flows per unit time. Sure, it is connected to the work done or power but is not the same thing. If you define gravitational potential difference as gH and water flow as dm/dt then to have power you have to have curent times this potential difference: gHdm/dt...
                                In a conductor, work is done also and energy per unit charge or potential difference is given by U (voltage) and current by dQ/dt so it seems to me that everything is same...






                                share|cite|improve this answer

























                                  up vote
                                  0
                                  down vote













                                  Power is defined as work done per unit time. So a mass of water moving from one potential to some other lower potetial can do work when it hits the wheel. How much work per unit time? It depends how much mass falls times height times gravitational constant g and all of that divided by time. Water current, on the other hand is just total volume or mass that flows per unit time. Sure, it is connected to the work done or power but is not the same thing. If you define gravitational potential difference as gH and water flow as dm/dt then to have power you have to have curent times this potential difference: gHdm/dt...
                                  In a conductor, work is done also and energy per unit charge or potential difference is given by U (voltage) and current by dQ/dt so it seems to me that everything is same...






                                  share|cite|improve this answer























                                    up vote
                                    0
                                    down vote










                                    up vote
                                    0
                                    down vote









                                    Power is defined as work done per unit time. So a mass of water moving from one potential to some other lower potetial can do work when it hits the wheel. How much work per unit time? It depends how much mass falls times height times gravitational constant g and all of that divided by time. Water current, on the other hand is just total volume or mass that flows per unit time. Sure, it is connected to the work done or power but is not the same thing. If you define gravitational potential difference as gH and water flow as dm/dt then to have power you have to have curent times this potential difference: gHdm/dt...
                                    In a conductor, work is done also and energy per unit charge or potential difference is given by U (voltage) and current by dQ/dt so it seems to me that everything is same...






                                    share|cite|improve this answer












                                    Power is defined as work done per unit time. So a mass of water moving from one potential to some other lower potetial can do work when it hits the wheel. How much work per unit time? It depends how much mass falls times height times gravitational constant g and all of that divided by time. Water current, on the other hand is just total volume or mass that flows per unit time. Sure, it is connected to the work done or power but is not the same thing. If you define gravitational potential difference as gH and water flow as dm/dt then to have power you have to have curent times this potential difference: gHdm/dt...
                                    In a conductor, work is done also and energy per unit charge or potential difference is given by U (voltage) and current by dQ/dt so it seems to me that everything is same...







                                    share|cite|improve this answer












                                    share|cite|improve this answer



                                    share|cite|improve this answer










                                    answered 3 hours ago









                                    Žarko Tomičić

                                    853511




                                    853511






















                                        up vote
                                        0
                                        down vote













                                        Water and current flow as well as other “mechanical” analogies (pipe resistance vs. electrical resistance, voltage vs. pressure, etc.) are useful for introducing electrical circuit concepts at an elementary level. This is because mechanical concepts are easier to visualize whereas electrical concepts are more abstract. The analogies can only go so far without a deeper understanding.



                                        Current does not equal electrical power and neither does water flow equal mechanical power.



                                        Electrical current ($frac {Coul}{s}$) times (in phase) voltage ($frac {J}{Coul}$) equals power ($frac {J}{s}$ = watts).



                                        Current flow ($frac {ft^3}{s}$) times pressure ($frac {lb-f}{ft^2}$) equals power ($frac {ft-lb}{s}$). ($frac {550 ft-lb}{s}=1 hp = 746 watts$)



                                        The water pressure for the water wheel can come from water dropping from a height above the wheel (potential energy) or even from a hose directed horizontally, depending on the orientation of the water wheel.



                                        To complete the analogy between current and water flow with respect to electrical an mechanical power, you need in addition the analogy between voltage (electrical potential) and pressure (mechanical potential).



                                        Hope this helps.






                                        share|cite|improve this answer

























                                          up vote
                                          0
                                          down vote













                                          Water and current flow as well as other “mechanical” analogies (pipe resistance vs. electrical resistance, voltage vs. pressure, etc.) are useful for introducing electrical circuit concepts at an elementary level. This is because mechanical concepts are easier to visualize whereas electrical concepts are more abstract. The analogies can only go so far without a deeper understanding.



                                          Current does not equal electrical power and neither does water flow equal mechanical power.



                                          Electrical current ($frac {Coul}{s}$) times (in phase) voltage ($frac {J}{Coul}$) equals power ($frac {J}{s}$ = watts).



                                          Current flow ($frac {ft^3}{s}$) times pressure ($frac {lb-f}{ft^2}$) equals power ($frac {ft-lb}{s}$). ($frac {550 ft-lb}{s}=1 hp = 746 watts$)



                                          The water pressure for the water wheel can come from water dropping from a height above the wheel (potential energy) or even from a hose directed horizontally, depending on the orientation of the water wheel.



                                          To complete the analogy between current and water flow with respect to electrical an mechanical power, you need in addition the analogy between voltage (electrical potential) and pressure (mechanical potential).



                                          Hope this helps.






                                          share|cite|improve this answer























                                            up vote
                                            0
                                            down vote










                                            up vote
                                            0
                                            down vote









                                            Water and current flow as well as other “mechanical” analogies (pipe resistance vs. electrical resistance, voltage vs. pressure, etc.) are useful for introducing electrical circuit concepts at an elementary level. This is because mechanical concepts are easier to visualize whereas electrical concepts are more abstract. The analogies can only go so far without a deeper understanding.



                                            Current does not equal electrical power and neither does water flow equal mechanical power.



                                            Electrical current ($frac {Coul}{s}$) times (in phase) voltage ($frac {J}{Coul}$) equals power ($frac {J}{s}$ = watts).



                                            Current flow ($frac {ft^3}{s}$) times pressure ($frac {lb-f}{ft^2}$) equals power ($frac {ft-lb}{s}$). ($frac {550 ft-lb}{s}=1 hp = 746 watts$)



                                            The water pressure for the water wheel can come from water dropping from a height above the wheel (potential energy) or even from a hose directed horizontally, depending on the orientation of the water wheel.



                                            To complete the analogy between current and water flow with respect to electrical an mechanical power, you need in addition the analogy between voltage (electrical potential) and pressure (mechanical potential).



                                            Hope this helps.






                                            share|cite|improve this answer












                                            Water and current flow as well as other “mechanical” analogies (pipe resistance vs. electrical resistance, voltage vs. pressure, etc.) are useful for introducing electrical circuit concepts at an elementary level. This is because mechanical concepts are easier to visualize whereas electrical concepts are more abstract. The analogies can only go so far without a deeper understanding.



                                            Current does not equal electrical power and neither does water flow equal mechanical power.



                                            Electrical current ($frac {Coul}{s}$) times (in phase) voltage ($frac {J}{Coul}$) equals power ($frac {J}{s}$ = watts).



                                            Current flow ($frac {ft^3}{s}$) times pressure ($frac {lb-f}{ft^2}$) equals power ($frac {ft-lb}{s}$). ($frac {550 ft-lb}{s}=1 hp = 746 watts$)



                                            The water pressure for the water wheel can come from water dropping from a height above the wheel (potential energy) or even from a hose directed horizontally, depending on the orientation of the water wheel.



                                            To complete the analogy between current and water flow with respect to electrical an mechanical power, you need in addition the analogy between voltage (electrical potential) and pressure (mechanical potential).



                                            Hope this helps.







                                            share|cite|improve this answer












                                            share|cite|improve this answer



                                            share|cite|improve this answer










                                            answered 1 hour ago









                                            Bob D

                                            1,932211




                                            1,932211






















                                                up vote
                                                0
                                                down vote













                                                The analogy with water actually holds really nicely if you consider a water wheel, or other hydroelectric system.



                                                But what you're missing is that the power produced does not only depend on the amount of water going past - it also depends on the speed at which it does so. (this makes sense for the hydro system because kinetic energy depends on velocity and mass)



                                                To make the analogy better, rather than thinking of the speed of the flow, think about how far it has fallen to aquire that speed. At this point you have a volume per second of water - the current - and you have a loss of height, which is literally a potential difference.






                                                share|cite|improve this answer

























                                                  up vote
                                                  0
                                                  down vote













                                                  The analogy with water actually holds really nicely if you consider a water wheel, or other hydroelectric system.



                                                  But what you're missing is that the power produced does not only depend on the amount of water going past - it also depends on the speed at which it does so. (this makes sense for the hydro system because kinetic energy depends on velocity and mass)



                                                  To make the analogy better, rather than thinking of the speed of the flow, think about how far it has fallen to aquire that speed. At this point you have a volume per second of water - the current - and you have a loss of height, which is literally a potential difference.






                                                  share|cite|improve this answer























                                                    up vote
                                                    0
                                                    down vote










                                                    up vote
                                                    0
                                                    down vote









                                                    The analogy with water actually holds really nicely if you consider a water wheel, or other hydroelectric system.



                                                    But what you're missing is that the power produced does not only depend on the amount of water going past - it also depends on the speed at which it does so. (this makes sense for the hydro system because kinetic energy depends on velocity and mass)



                                                    To make the analogy better, rather than thinking of the speed of the flow, think about how far it has fallen to aquire that speed. At this point you have a volume per second of water - the current - and you have a loss of height, which is literally a potential difference.






                                                    share|cite|improve this answer












                                                    The analogy with water actually holds really nicely if you consider a water wheel, or other hydroelectric system.



                                                    But what you're missing is that the power produced does not only depend on the amount of water going past - it also depends on the speed at which it does so. (this makes sense for the hydro system because kinetic energy depends on velocity and mass)



                                                    To make the analogy better, rather than thinking of the speed of the flow, think about how far it has fallen to aquire that speed. At this point you have a volume per second of water - the current - and you have a loss of height, which is literally a potential difference.







                                                    share|cite|improve this answer












                                                    share|cite|improve this answer



                                                    share|cite|improve this answer










                                                    answered 39 mins ago









                                                    Flyto

                                                    46845




                                                    46845






















                                                        up vote
                                                        0
                                                        down vote













                                                        Power to a water-wheel depends both on the current (amount of water delivered)
                                                        and the head (vertical drop of water as it turns the wheel). So, the
                                                        water analogy does have TWO variables that multiply together to make
                                                        power: current, measuring (for instance) the water flow at Niagara,
                                                        and vertical drop (like the height of Niagara Falls).



                                                        Current is NOT the same as power, in a river, because long stretches of
                                                        moving water in a channel don't dissipate energy as much as a waterfall does.
                                                        Siting a hydroelectric power plant at Niagara Falls makes sense.
                                                        In the analogy to electricity, a wire can deliver current at little voltage
                                                        drop (and has tiny power dissipation) but a resistor which has that same
                                                        current will be warmed (it has a substantial terminal-to-terminal voltage drop).






                                                        share|cite|improve this answer

























                                                          up vote
                                                          0
                                                          down vote













                                                          Power to a water-wheel depends both on the current (amount of water delivered)
                                                          and the head (vertical drop of water as it turns the wheel). So, the
                                                          water analogy does have TWO variables that multiply together to make
                                                          power: current, measuring (for instance) the water flow at Niagara,
                                                          and vertical drop (like the height of Niagara Falls).



                                                          Current is NOT the same as power, in a river, because long stretches of
                                                          moving water in a channel don't dissipate energy as much as a waterfall does.
                                                          Siting a hydroelectric power plant at Niagara Falls makes sense.
                                                          In the analogy to electricity, a wire can deliver current at little voltage
                                                          drop (and has tiny power dissipation) but a resistor which has that same
                                                          current will be warmed (it has a substantial terminal-to-terminal voltage drop).






                                                          share|cite|improve this answer























                                                            up vote
                                                            0
                                                            down vote










                                                            up vote
                                                            0
                                                            down vote









                                                            Power to a water-wheel depends both on the current (amount of water delivered)
                                                            and the head (vertical drop of water as it turns the wheel). So, the
                                                            water analogy does have TWO variables that multiply together to make
                                                            power: current, measuring (for instance) the water flow at Niagara,
                                                            and vertical drop (like the height of Niagara Falls).



                                                            Current is NOT the same as power, in a river, because long stretches of
                                                            moving water in a channel don't dissipate energy as much as a waterfall does.
                                                            Siting a hydroelectric power plant at Niagara Falls makes sense.
                                                            In the analogy to electricity, a wire can deliver current at little voltage
                                                            drop (and has tiny power dissipation) but a resistor which has that same
                                                            current will be warmed (it has a substantial terminal-to-terminal voltage drop).






                                                            share|cite|improve this answer












                                                            Power to a water-wheel depends both on the current (amount of water delivered)
                                                            and the head (vertical drop of water as it turns the wheel). So, the
                                                            water analogy does have TWO variables that multiply together to make
                                                            power: current, measuring (for instance) the water flow at Niagara,
                                                            and vertical drop (like the height of Niagara Falls).



                                                            Current is NOT the same as power, in a river, because long stretches of
                                                            moving water in a channel don't dissipate energy as much as a waterfall does.
                                                            Siting a hydroelectric power plant at Niagara Falls makes sense.
                                                            In the analogy to electricity, a wire can deliver current at little voltage
                                                            drop (and has tiny power dissipation) but a resistor which has that same
                                                            current will be warmed (it has a substantial terminal-to-terminal voltage drop).







                                                            share|cite|improve this answer












                                                            share|cite|improve this answer



                                                            share|cite|improve this answer










                                                            answered 17 mins ago









                                                            Whit3rd

                                                            6,29621225




                                                            6,29621225






















                                                                up vote
                                                                0
                                                                down vote













                                                                I'd like to put what others said already into equations:



                                                                A river has mass flow rate $dot m$ (kg/s) (the "current"). The water flows with velocity $v$ (m/s). Power is the kinetic energy that is carried per unit time:



                                                                $$
                                                                dot W = frac{dot m v^2}{2}
                                                                $$

                                                                and notice that this has proper units of watt. If we take "voltage" to be $v^2/2$, then we get
                                                                $$
                                                                text{(power)} = text{(current)}timestext{(voltage)}
                                                                $$



                                                                Notice that the mass flow rate is not enough to give you high power. When the river is wide the velocity is low. If you want the water wheel to run fast you should build it at a narrow passage.






                                                                share|cite|improve this answer

























                                                                  up vote
                                                                  0
                                                                  down vote













                                                                  I'd like to put what others said already into equations:



                                                                  A river has mass flow rate $dot m$ (kg/s) (the "current"). The water flows with velocity $v$ (m/s). Power is the kinetic energy that is carried per unit time:



                                                                  $$
                                                                  dot W = frac{dot m v^2}{2}
                                                                  $$

                                                                  and notice that this has proper units of watt. If we take "voltage" to be $v^2/2$, then we get
                                                                  $$
                                                                  text{(power)} = text{(current)}timestext{(voltage)}
                                                                  $$



                                                                  Notice that the mass flow rate is not enough to give you high power. When the river is wide the velocity is low. If you want the water wheel to run fast you should build it at a narrow passage.






                                                                  share|cite|improve this answer























                                                                    up vote
                                                                    0
                                                                    down vote










                                                                    up vote
                                                                    0
                                                                    down vote









                                                                    I'd like to put what others said already into equations:



                                                                    A river has mass flow rate $dot m$ (kg/s) (the "current"). The water flows with velocity $v$ (m/s). Power is the kinetic energy that is carried per unit time:



                                                                    $$
                                                                    dot W = frac{dot m v^2}{2}
                                                                    $$

                                                                    and notice that this has proper units of watt. If we take "voltage" to be $v^2/2$, then we get
                                                                    $$
                                                                    text{(power)} = text{(current)}timestext{(voltage)}
                                                                    $$



                                                                    Notice that the mass flow rate is not enough to give you high power. When the river is wide the velocity is low. If you want the water wheel to run fast you should build it at a narrow passage.






                                                                    share|cite|improve this answer












                                                                    I'd like to put what others said already into equations:



                                                                    A river has mass flow rate $dot m$ (kg/s) (the "current"). The water flows with velocity $v$ (m/s). Power is the kinetic energy that is carried per unit time:



                                                                    $$
                                                                    dot W = frac{dot m v^2}{2}
                                                                    $$

                                                                    and notice that this has proper units of watt. If we take "voltage" to be $v^2/2$, then we get
                                                                    $$
                                                                    text{(power)} = text{(current)}timestext{(voltage)}
                                                                    $$



                                                                    Notice that the mass flow rate is not enough to give you high power. When the river is wide the velocity is low. If you want the water wheel to run fast you should build it at a narrow passage.







                                                                    share|cite|improve this answer












                                                                    share|cite|improve this answer



                                                                    share|cite|improve this answer










                                                                    answered 11 mins ago









                                                                    Themis

                                                                    2895




                                                                    2895






























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