According to plumbing analogy I've hard time seeing why power is measured in volts*amps, instead of just amps.
I found an analogy from http://science.howstuffworks.com/environmental/energy/question501.htm
Electrical power is measured in watts. In an electrical system power (P) is equal to the voltage multiplied by the current.
The water analogy still applies. Take a hose and point it at a waterwheel like the ones that were used to turn grinding stones in watermills. You can increase the power generated by the waterwheel in two ways. If you increase the pressure of the water coming out of the hose, it hits the waterwheel with a lot more force and the wheel turns faster, generating more power. If you increase the flow rate, the waterwheel turns faster because of the weight of the extra water hitting it.
This explanation contrasts two ways of increasing the power:
- increasing the pressure [volts] or
- increasing the flow rate [amps].
But increasing the pressure also increases the flow rate!? What am I missing here?
Would it be more precise to say that I can increase the power by:
- increasing the pressure [volts] while keeping flow rate [amps] the same (by using hose with smaller diameter [increasing resistance]) or
- increasing the flow rate [amps] while keeping the pressure [volts] the same (by using hose with bigger diameter [decreasing resistance]?
Does increasing water pressure while reducing hose diameter (so that flow rate stays the same) really give you more powerful waterwheel?