120V Power

[Josh2008]

I've been told that electricity can be compared to the fundamentals of hydraulics.

Power = Pressure X Flow
as
Power = Voltage X Current

When there is a change in pressure, flow exists...
When there is a change in voltage, electrons flow (current exists)...

When im thinking hyrdaulics, I prefer to think when a pump creates flow, or pumps fluid through pipes, pressure is created due to the resistance to flow. Therefore you cannot create pressure without resistance to flow.

This concept is hard to understand thinking about the power grid. Here in Canada it is 120V @ 60Hz.

So now I think, to create voltage there must be a resistance to current. Does this make sense? If I have 120V available at my house outlet and I have no load plugged in (such as running a TV) how is there 120V?

Maybe its like you can create pressure if there is nowhere for the fluid to escape. So maybe thats how 120V is available at the house outlets? Is the relationship between hydraulics and electricity valid particularly in direct current systems and not AC?

Does everything that is plugged into the outlet use 120V with different currents?

I'm confused, please help explain.

 

[desertfox]

Hi josh2008

Read this link:-

http://www.upscale.utoronto.ca/IYearLab/SimpleCircuits.pdf

Yes there is a resistance to current which creates a voltage
drop across the resistor.

desertfox

 

[ccjersey]

Your hydraulic analogy is pretty good except for the statement that you cannot create voltage without resistance.

Think of pressurized air or a hydraulic accumulator with a nitrogen charge on top of the fluid. You can have a static pressure (like voltage) even though there is no flow of air or fluid (current).

 

[LionelHutz]

Think about these comparisons and maybe they will help.

Hydraulics - a closed pipe is infinite resistance = no flow
Electrical - an open electrical circuit is infinite resistance = no current flow

Hydraulics - a closed pipe creates maximum pressure
Electrical - a open circuit allows maximum voltage

Hydraulics - a open pipe has no resistance to flow = no pressure and maximum flow
Electical - a short circuit has no resistance = no voltage and maximum curent flow

 

[PHovnanian]

If I have 120V available at my house outlet and I have no load plugged in (such as running a TV) how is there 120V?

It this case you have infinite resistance (well, actually hundreds of megohoms).

 

[jraef]

If an electron falls out of your outlet onto the floor and no stereo is there to make use of it, did it make any sound?

 

[rbulsara]

Josh's thinking is not entirely flawed. Open circuit voltage is the voltage against infinite resistance. There is no need to have the current just the tendency to create current which is pressure.

Open circuit voltage is akin to static head (pressure) of a hydro dam. Immense pressure can exist with out a flow.

Resistnace is always needed to control the flow and maintain the voltage. Zero or close to zero resistance tend to neuralize the voltage diffrenece and produce almost infinite current. Just like what would happen if the dam breaks!

It is true that without resistance you cannot maintain the voltage! Voltage drop across a resistance is not "generation" voltage just the drop like a pressure drop over a restriction.







Rafiq Bulsara

http://www.srengineersct.com

 

[rbulsara]

I just noticed, Phovnanian said the same thing.

Rafiq Bulsara

http://www.srengineersct.com

 

[PHovnanian]

I just noticed, Phovnanian said the same thing.

Great minds think alike.

Or you got hold of my prescription somehow.
;-)

 

[rbulsara]

PHovnanian:
Could be the latter.. but let's stick with the former!

Rafiq Bulsara

http://www.srengineersct.com

 

[amptramp]

It is important to the understanding of the analogies to distinguish between power supplied versus power absorbed. The voltage present at the wall outlet is a power supply (potential energy) whereas the voltage measured across a load, i.e., a resistor or lightbulb (in concert with the current flow through the resistor) is a utilization (drop) of power.

 

[Rylee]

The current drawn on a 120V outlet is in direct proportion to the resistance. V=IR where V=voltage (120) I=Current and R=Resistance in Ohms.
The voltage drop across the resistor (load) will be consistant - 120V assuming a line to neutral connection. If R approaches zero, I approached infinity.

Hope this helps

 

[Rylee]

One more thing, Voltage times Current = Load (Watts)
So a 100W lamp will draw a current of 100W/120V = 0.83Amps
So the resistance of the lamp can be calculated using V=IR so 120=0.83R so R = 144 Ohms

Base Builders, LLC

http://www.basebuilders.com

 

[racobb]

Voltage times Current = va. Only equals watts if the load is purely resistive.

Alan