Voltage V.S. Amperage

[Fl_Richard]

Lots of people don't understand the difference between voltage and amperage. I've got a good analogy that may help some to understand the differences.

As compared to a flowing river:

Amperage is the volume of water flowing down stream, whether deep or wide.

Voltage is the speed the water is traveling.

So a narrow creek flowing rapidly (12-14 volts) may not have enough flow (amperage or current) to rapidly fill the reservoir (turn starter) even though it's flowing fast (12 volts)

A wide creek flowing flowing slowly (10 volts and good cabling) may not have enough voltage to fill the reservoir fast enough (turn starter quickly).

I hope this analogy helps some people understand the differences between voltage (speed) and current (volume). It's enlightened several friends.

Cheers!!
Richard

 

[ebry710]

Re: Voltage V.S. Amperage

Lots of people don't understand the difference between voltage and amperage. I've got a good analogy that may help some to understand the differences.

As compared to a flowing river:

Amperage is the volume of water flowing down stream, whether deep or wide.

Voltage is the speed the water is traveling.

So a narrow creek flowing rapidly (12-14 volts) may not have enough flow (amperage or current) to rapidly fill the reservoir (turn starter) even though it's flowing fast (12 volts)

A wide creek flowing flowing slowly (10 volts and good cabling) may not have enough voltage to fill the reservoir fast enough (turn starter quickly).

I hope this analogy helps some people understand the differences between voltage (speed) and current (volume). It's enlightened several friends.

Cheers!!
Richard

I am garden hose guy. I look at voltage as pressure of the hose and amps as amount and direction of flow.

 

[F_R]

Re: Voltage V.S. Amperage

The third part of the equation is resistance.
E=IR
I=E/R
R=E/I

E is Voltage (Electromotive Force)
I is Current
R is Resistance

The above is Ohm's Law. Once you figure that out, you are ready for Lesson Two.

 

[tx1961whaler]

Re: Voltage V.S. Amperage

The third part of the equation is resistance.
E=IR
I=E/R
R=E/I

E is Voltage (Electromotive Force)
I is Current
R is Resistance

The above is Ohm's Law. Once you figure that out, you are ready for Lesson Two.

Agree. The first two analogies do not take into account resistance, which is both a "voltage dropper" and a current limiter. The hose analogy works, if you put valves at the end and several place in the middle and call it resistance. The stream analogy works if you put dams in the streams, and ignore flooding

 

[ebry710]

Re: Voltage V.S. Amperage

Agree. The first two analogies do not take into account resistance, which is both a "voltage dropper" and a current limiter. The hose analogy works, if you put valves at the end and several place in the middle and call it resistance. The stream analogy works if you put dams in the streams, and ignore flooding

Sure. resistance is the diameter of the hose. BTW. The hose analogy was brought to me via college physics and has just stayed with me for 30 years. It makes it easier to tutor ohms law. Some of us our just simple that way.

 

[jhebert]

Re: Voltage V.S. Amperage

...I've got a good analogy that may help some to understand the differences.

As compared to a flowing river:

Amperage is the volume of water flowing down stream, whether deep or wide.

Voltage is the speed the water is traveling.

Unfortunately, your analogy is not correct. A better analogy of the relationship of electrical units like voltage, current, and resistance, to the flow of water in a pipe is given at

http://hyperphysics.phy-astr.gsu.edu/HBASE/electric/watcir.html

Voltage is analogous to the pressure which drives the flow of water. You can see this at a dam. The head of water behind the dam creates a pressure in the water which is analogous to electrical voltage

The electrical current is analogous to the rate of flow of a particular volume of water, such as a certain number of gallons per hour--not just the volume. It is not proportional to the speed of water movement. The volume of water is analogous to the electrical charge.

In electrical circuits the motion of the charge is generally near the speed of light, and is called the propagation velocity. The speed of movement of water is analogous to the propagation velocity, but as we know, this is at much lower speeds.

Also see:

http://www.cns.cornell.edu/cipt/labs/documents/webWaterCircuits.pdf

 

[ebry710]

Re: Voltage V.S. Amperage

Unfortunately, your analogy is not correct. A better analogy of the relationship of electrical units like voltage, current, and resistance, to the flow of water in a pipe is given at

http://hyperphysics.phy-astr.gsu.edu/HBASE/electric/watcir.html

Voltage is analogous to the pressure which drives the flow of water. You can see this at a dam. The head of water behind the dam creates a pressure in the water which is analogous to electrical voltage

The electrical current is analogous to the rate of flow of a particular volume of water, such as a certain number of gallons per hour--not just the volume. It is not proportional to the speed of water movement. The volume of water is analogous to the electrical charge.

In electrical circuits the motion of the charge is generally near the speed of light, and is called the propagation velocity. The speed of movement of water is analogous to the propagation velocity, but as we know, this is at much lower speeds.

Also see:

http://www.cns.cornell.edu/cipt/labs/documents/webWaterCircuits.pdf

Nice explanation.

 

[TerryMSU]

Re: Voltage V.S. Amperage

In electrical circuits the motion of the charge is generally near the speed of light, and is called the propagation velocity. The speed of movement of water is analogous to the propagation velocity, but as we know, this is at much lower speeds.

Also see:

http://www.cns.cornell.edu/cipt/labs/documents/webWaterCircuits.pdf

Very close, but one minor bit of trivia. Propagation velocity is not the speed of the electrons. A better analogy for propagation velocity is to take a 1/2 inch copper pipe and stuff it full of marbles. When you stuff a new marble in at one end, a different marble comes out of the other end instantaneously. The time for the new marble to come out the other end is called drift velocity, and that is MUCH slower than the speed of light. However, this in no way affects the real behavior of ohms law.

In addition to ohms law, there is watts law, which defines the power to (or from) any element in the system.

P is power in watts, I is current in amps, V is volatge in amps, and R is resistance in ohms.

P = I times V = I squared * R = V squared divided by R

Another bit of trivia is 746 watts is the equavalent of 1 horsepower. Thatrb is why you cannot run a 10 HP electrical motor on a 12 volt battery (current required is 622 amps at 12 volts => 7460 watts => 10 HP

TerryMSU

 

[jhebert]

Re: Water Analogies for Voltage and Current

Re: Water Analogies for Voltage and Current

Terry--Thank you for that emendation.

An application of a water analogy might be like this, and since I think you are also a fellow Michiganian, you may be familiar with it:

The head of the Detroit River is normally about three feet higher than the mouth of the Detroit river. This difference in the height of the water is the "voltage." Water flows down the Detroit River at a particular speed, and this speed, in combination with the volume of water, produces a certain rate of flow (in gallons per second). The rate of flow is the analogous "current"

Here we have to be careful not to confuse the electrical current with the speed of the water flow, also called the current. The water current speed is part of the rate of flow, but it is the rate of flow in gallons per second that is analogous to an electrical current.

"Water levels fall about 3 ft though Detroit River, which has an average
discharge of 186,000 ft3/s."

Source: http://mi.water.usgs.gov/progproj/SCDInfoSheet.pdf

Connecting the head of the Detroit River and the mouth of the Detroit river are many passages. Each passage can be thought of as having a "resistance." These passages are in some cases connected in parallel. For example in the lower Detroit River the water flows around the large island of Grosse Ile, as well as several smaller islands like Bois Blanc Island. The passages have various depths. The deeper passages conduct a higher rate of flow in gallons per second than the shallower passages. In this way the analogy is exactly like an electrical circuit. Current flow for a give voltage is always greater in the lower resistance branch of the circuit.

During the spring we see more water coming down from the upper lakes. This water tends to build up and raises the level at the head of the river. This is analogous to an increase in the voltage. This causes the rate of flow in the river to increase. The gallons-per-second flow rate will increase.

If the river has become blocked with ice or snags, its "resistance" increases. This means that the flow rate will decrease. Again, analogous to electrical circuits.

 

[Wee Hooker]

Re: Voltage V.S. Amperage

Wow, I'm betting this has turned into an answer he didn't expect ;-)
Too many engineers in the kitchen