Al, Thanks again for your response. Thanks, Jim. Regarding...
Am I correct in assuming watts is a measurement of electrical energy? Watts is a unit of power, as you of course realize. Power is a quantity that is defined at a specific instant of time, although its average value over some interval of time can of course be calculated. Energy is defined as the product (multiplication) of power and time, and can be expressed as some number of joules, as well as in various other units. Well I knew watts is a unit of power and I somewhat understood energy and joules. But I guess I didn’t understand the real differences between the two. I do have a better understanding now thanks to you Al. . The electrical energy will be greater at 120V than at 24V for a circuit using the same 2 amp fuse for overcurrent protection.
120V x 2A = 240 watts
24V x 2A = 48 watts
240V x 2A = 480 watts The power and the energy being conveyed to the load will of course be much greater in the 120 and 240 volt cases than in the 24 volt case. But as I’m sure you realize but others may not, the only voltage that the fuse "knows about" is the one that appears between its two terminals, which when it is not blown corresponds to the amount of current it is conducting times its resistance. In the case of audio equipment operating normally that voltage will typically be a small fraction of a volt.
Quote: "But as I’m sure you realize but others may not, the only voltage that the fuse "knows about" is the one that appears between its two terminals, which when it is not blown corresponds to the amount of current it is conducting times its resistance." " times its resistance." I have not ever heard it explained that way before. I honestly have never measured a voltage across the end caps or blades of a good fuse. A blown fuse on the other hand yes, as you stated. I have measured a slight voltage drop across the fuse holder clips, mostly cartridge fuses. A VD across the fuse holder clips indicates poor contact pressure and or corrosion, poor surface area between the fuse caps and fuse holder clips. The only fuse I have on hand is a 4 amp slow blow fuse. I have an older model Fluke 87 True RMS multimeter and I checked for resistance across the fuse link end caps. With the meter set on ohms auto first touching the two probes together the meter reads 000.01 ohm. I got the same exact reading checking the fuse. LOL, I even reversed the fuse and got the same reading. (You know who that was for) I have read posts of guys that buy audio grade fuses that say they do indeed measure a resistance across the fuse link end caps. What you said above does make sense though. I have a good basic understanding how the electromagnetic wave thingy works, I just need learn the lingo better how to express it. Me thinks when talking about electrical power issues and electrical safety codes, like NEC, I will stick with the old school way I was taught and have a good understanding of. Besides that is what the majority of people understand. Especially electricians. As for ICs and speaker cables the old school theory just doesn’t fit the reality of how the audio signal travels from the source to the load. Thanks again Al for all your help, Jim . |
@kijanki, Thank you for your informative response.
From what I understand the movement of the current in the conductor is quite slow.... Correct?
Electric
current is a flow of electric charge and not the flow of electrons.
(In fluids electric charge is carried by ions and not the electrons).
Number of electrons crossing given point defines amount of electric
charge (current) passing. Motion of electric charge is usually
explained as a row of stacked balls in the tube - when you push them
slowly they will move slowly but when you hit the first one with a
hammer the last one will respond instantly - that's the speed of
electric current (charge). Of course there is plenty of space between
electrons but "stacking" is not physical but electrical (electric
charge).
Quote from link below.
Electric current is not a flow of energy; it's a flow of charge. Charge
and energy are two very different things. To separate them in
your mind, see this
list of differences.
An electric current is a flowing motion of charged particles, and the
particles do not carry energy along with them as they move. A current is
defined as a flow of charge by I=Q/T; amperes are coulombs of charge
flowing per unit time. The term "Electric Current" means the same thing
as "charge flow." Electric current is a very slow flow of charges,
while energy flows fast. Also, during AC alternating current the
charges
move slightly back and forth while the energy moves rapidly
forward.
Electric energy is quite different than charge. The energy
traveling across an electric current is made up of waves in
electromagnetic fields and it moves VERY rapidly. Electric energy moves
at a completely different speed than electric current, and obviously they
are two different things flowing in wires at the same time. Unless we
realize that two different things are flowing, we won't understand how
circuits work. Indeed, if we believe in a single flowing "electricity,"
we will have little grasp of basic electrical
science.
In an electric circuit, the path of the electric charges is circular,
while the path of the energy is not. A battery can send electric energy
to a light bulb, and the bulb changes electrical energy into light. The
energy does not flow back to the battery again. At the same time,
the electric current is different; it is a very slow circular flow, and
the electric charges flow through the light bulb filament and all of them
flow back out again. They return to the battery.
The term "Electric Current" means the same thing
as "charge flow." Electric current is a very slow flow of charges,
while energy flows fast. Also, during AC alternating current the
charges
move slightly back and forth while the energy moves rapidly
forward.
The
energy does not flow back to the battery again. At the same time,
the electric current is different; it is a very slow circular flow, and
the electric charges flow through the light bulb filament and all of them
flow back out again. They return to the battery.
http://amasci.com/miscon/eleca.html#cflowAfter reading your post I went back and checked again what I had read. Then I clicked on the blue high lighted "slow" word. And this came up.
The quick answer
Inside the wires, the "something" moves very, very slowly, almost as
slowly as the minute hand on a clock. Electric current is like slowly
flowing water inside a hose. Very slow, so perhaps a flow of
syrup. Even maple syrup moves too fast, so that's not a good analogy.
Electric charges typically flow as slowly as a river of warm putty. And
in AC
circuits, the moving charges don't move forward at all, instead they sit
in one place and vibrate. Energy can only flow rapidly in an electric
circuit because metals are already filled with this "putty." If we push
on one end of a column of putty, the far end moves almost instantly. Energy
flows fast, yet an electric current is a very slow flow.
Then,
The complicated answer
Within all metals there is a substance which can move. This stuff has
several different names: the Sea of Charge, or the Electron Sea, or the
Electron Gas, or "charge." We often call it "electricity," and state
that electric currents are flows of electricity. Calling it
"electricity" can be misleading because many people believe that
electricity is a form of energy, yet charge is not energy, and currents
are not flows of energy. Also it can be misleading because the Sea of
Charge
exists within in all metal objects, all the time, even when the metal
hasn't been made into a wire and is not part of an electric device. If the
Electron Sea is "electricity," then we must say that all metals are
always full of electricity, and that batteries are simply
electricity-pumps. Better to call it by the name "charge-sea," and avoid
the misleading word "electricity" entirely.
During an electric current, the metal wire stays still and the sea of
charge flows along through it. When the flashlight switch is turned off
and the lightbulb goes dark, the charge-sea stops moving forward. Even
though it stops moving, the charge-sea is still inside of that wire. If
the flashlight is again turned on, but then two light bulbs are connected
in
parallel instead of one, the electric current will have twice
as large a
value, and twice as much light will be created. And most important, the
charge-sea within the battery's wires will flow twice as fast. In other
words, the speed of the charges is proportional to the value of
electric current; small current means slow charge-flow, large
current means
high speed. Zero current means the charges have stopped in place. Note
however
that an electric current does not have just one speed within any circuit.
Charges speed up whenever they flow into a thinner wire. The high current
in a large flash-lantern's lightbulb will be much faster than the same
current in the other conductors in the lantern. Even though an electric
current is a very slow flow of charges, we can't know the actual speed of
flow unless first we know the thickness of the wires, as well as the
*value* (the amperes) of the current in the wires.
Quote:
"In other
words, the speed of the charges is proportional to the value of
electric current; small current means slow charge-flow, large
current means
high speed. Zero current means the charges have stopped in place. Note
however
that an electric current does not have just one speed within any circuit.
Charges speed up whenever they flow into a thinner wire. The high current
in a large flash-lantern's lightbulb will be much faster than the same
current in the other conductors in the lantern. Even though an electric
current is a very slow flow of charges, we can't know the actual speed of
flow unless first we know the thickness of the wires, as well as the
*value* (the amperes) of the current in the wires. " And then he says,
The speed of electric current
Since nothing visibly moves when the charge-sea flows, we cannot measure
the speed of its flow by eye. Instead we do it by making some
assumptions and doing a calculation. Let's say we have an electric
current in normal lamp cord connected to bright light bulb. The electric
current works out to be a flow of approximatly 3 inches per hour. Very
slow!
http://amasci.com/miscon/speed.htmlWow! I'll have to reread it again tomorrow. But I think he is saying the same thing you said. At least some parts of what he is saying. But not others? Thanks again for your response, Jim |
Correction: In my post dated 09-01-2017 8:33pm The only fuse I have on hand is a 4 amp slow blow fuse. I have an older model Fluke 87 True RMS multimeter and I checked for resistance across the fuse link end caps.
With the meter set on ohms auto first touching the two probes together the meter reads 000.01 ohm. That should read, meter reads 000.1 ohm. . |
Jea48, It is all very confusing. AFAIK electric current (as motion of electric charge) in wire moves very fast - close to speed of light. Individual electrons also travel fast at about 1% of the light speed (2000km/s) but they move in different directions. What moves really slow is average speed of all electrons (drift velocity). Back to our analogy with balls stacked in the tube - last ball will start moving the same moment as first ball (they push each other). That's electric charge moving (electric current) at the speed of light. |
The "electron drift" IS the electron velocity. Drift velocity is on the order of cm per hour. In other words they, the electrons, are virtually stationary. The "drift velocity" is not (rpt not) the net velocity due to back and forth motion of the electrons. Whatever moves at lightspeed or near lightspeed are photons. You know, the only particles that can - and must - travel at lightspeed or near lightspeed. If you want to say current is an EM wave and therefore comprises photons I have no problem with that. Thus electrons are charge carriers, they are not the charge per se.
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