Ohm Law again

[arc]

!

Moderator Note

This thread is a branch. To discuss multimeter reading on Logitech speaker go back to original thread.

 

 

An ohm meter uses an internal battery to measure resistance.

 

If you put it across a power source it's no wonder the reading is all over the place, it's modulating according to the power used in the circuit.

 

Ohms law doesn't work that way. It's used to calculate a missing variable of either volts, amps or ohms (resistance)

 

E = Volts (volume)

I = Amps (pressure)

R = Ohms (resistance)

 

 

 

E = Volts (pressure)

I = Amps (volume) aka current

R = Ohms (resistance)

Edited November 23, 2015 by imatfaal
mod

[Lagoon Island Pearls]

 

E = Volts (pressure)

I = Amps (volume) aka current

R = Ohms (resistance)

 

Volts is to gallons as amps is to PSI. We all know it's not the volume that can kill you, it's the pressure.

 

If you pour a bucket of water over your head, you get wet. If you run a small amount of water though a pressure washer, you can cut your arm off.

When you use a garden hose, full flow (volume) does not have much effect. Hold your finger over the end (resistance) increases pressure (amps) but reduces volume (volts).

If you increase the voltage of a circuit, amps drop. If you lower the voltage, amps rise.

 

That's why it's bad to run tools with weak batteries (low volts), because they'll burn out because they are running high amps.

 

Inversely, circuits rated at say 12 volts can run up to 30 or more volts without any problems, because there's less amps.

Voltage is the amount of potential energy between two points on a circuit.

You can stand up to your head in a river with high volume and low current, but a small stream with high current can sweep you off your feet.

Edited November 22, 2015 by Lagoon Island Pearls

[arc]

 

Volts is to gallons as amps is to PSI. We all know it's not the volume that can kill you, it's the pressure.

 

If you pour a bucket of water over your head, you get wet. If you run a small amount of water though a pressure washer, you can cut your arm off.

When you use a garden hose, full flow (volume) does not have much effect. Hold your finger over the end (resistance) increases pressure (amps) but reduces volume (volts).

 

Are you sure about that? . . . .When you turn up the heat on an electric appliance, lets say a stove, does the voltage go up or the amperage (current). You say voltage, what type of control on the stove increases and decreases the voltage?

 

Hint: The voltage is the same on both sides of the heating element, even lower. You know there is a term called voltage drop?

[Lagoon Island Pearls]

 

Are you sure about that? . . . .When you turn up the heat on an electric appliance, lets say a stove, does the voltage go up or the amperage (current). You say voltage, what type of control on the stove increases and decreases the voltage?

 

Hint: The voltage is the same on both sides of the heating element, even lower. You know there is a term called voltage drop?

 

Turning up the heat on an electric stove is done by reducing resistance. Seeing it's plugged into 120 or 220 that remains constant, hence the amps rise.

Actually were, missing a point. Inductive and resistive loads behave differently. Technically, we're both correct.

[arc]

It makes it difficult to discuss the subject if you go back and edit your post after reading my response to it. I quoted your entire post, why did you change it? Paint yourself into a corner?

[Lagoon Island Pearls]

It makes it difficult to discuss the subject if you go back and edit your post after reading my response to it. I quoted your entire post, why did you change it? Paint yourself into a corner?

 

No, for clarity and I added other points.

 

What I should have done was open my comments with... in an inductive circuit... because the OP is working with one.

[arc]

Well, I'm off to bed, you can go ahead and edit to your hearts content. . . . . . . . . . . . .I'm just messing with you. You got on some thin ice though, your feet must be soaked.

[Lagoon Island Pearls]

It makes it difficult to discuss the subject if you go back and edit your post after reading my response to it. I quoted your entire post, why did you change it? Paint yourself into a corner?

 

I edited while you were responding, (once at 1123 my time and again at 1202) not afterwards. Your response posted a minute after that. I edited nothing since.

[John Cuthber]

This post is wrong in just about every important respect

 

Volts is to gallons as amps is to PSI. We all know it's not the volume that can kill you, it's the pressure.

 

If you pour a bucket of water over your head, you get wet. If you run a small amount of water though a pressure washer, you can cut your arm off.

When you use a garden hose, full flow (volume) does not have much effect. Hold your finger over the end (resistance) increases pressure (amps) but reduces volume (volts).

If you increase the voltage of a circuit, amps drop. If you lower the voltage, amps rise.

 

That's why it's bad to run tools with weak batteries (low volts), because they'll burn out because they are running high amps.

 

Inversely, circuits rated at say 12 volts can run up to 30 or more volts without any problems, because there's less amps.

Voltage is the amount of potential energy between two points on a circuit.

You can stand up to your head in a river with high volume and low current, but a small stream with high current can sweep you off your feet.

[Lagoon Island Pearls]

This post is wrong in just about every important respect

So you mean to say it's volts that kill you and not amps? Citation please.

 

Volts are not the amount of potential energy between two points? Citation please.

 

Volts rise with amps? Citation please.

 

Incidentally if you want to talk about inductive circuits, why introduce resistance as in post3?

 

I stand corrected.

[John Cuthber]

So you mean to say it's volts that kill you and not amps? Citation please.

 

Volts are not the amount of potential energy between two points? Citation please.

 

Volts rise with amps? Citation please.

 

 

"So you mean to say it's volts that kill you and not amps? Citation please."

No.

I mean that since the ratio of the voltage to the current is practically constant, you can't have one without the other.

It's called Ohm's law. I think there might be a thread about it somewhere.

 

Also, what kills you isn't volts or amps or even power or even energy delivered but some rather complicated function of energy and time.

 

"Volts are not the amount of potential energy between two points? Citation please."

That's the one thing you got right

"Volts rise with amps?"

Yes, and once again, it's Ohm's law.

 

If you insist on using the water flow analogy.

If I have a long thin hose pipe and feed it from a tank of water there's a small flow rate. If I use a deeper tank and get a higher pressure then there's a faster flow.

 

Do you really think that raising the pressure reduces the flow rate?

[Lagoon Island Pearls]

"Volts rise with amps?"

Yes, and once again, it's Ohm's law.

 

In Ohm's law volts and amps are inversely proportional to resistance

Do you really think that raising the pressure reduces the flow rate?

 

Do you really think that restricting the flow rate doesn't increase pressure?

[studiot]

But does the member OP need a discussion of Ohm's Law?

 

Doesn't he needs a new mains adapter and/or a new multimeter?

[Lagoon Island Pearls]

But does the member OP need a discussion of Ohm's Law?

 

Ohms law doesn't work that way. It's used to calculate a missing variable of either volts, amps or ohms (resistance)

 

I should have left the parenthesis out, for simplicity.

 

Doesn't he needs a new mains adapter and/or a new multimeter?

 

Most multi-meters are 9 volts nowadays. If it were 1.5v like the old days, he would have at least buried the needle past zero.

[John Cuthber]

 

In Ohm's law volts and amps are inversely proportional to resistance

 

FFS learn simple algebra. Voltage is proportional to resistance. V=IR

 

 

 

Do you really think that restricting the flow rate doesn't increase pressure?

Yes, because there is no way in which it can (except momentarily when the flow changes abruptly)

The cold water supply in my house is fed from a tank in the roof.

The water runs through a pipe to the tap. It's about 3 metres or so of drop, so the pressure at the tap is about 3 metres of water (you can convert that to other units if you like)

On the other side of the tap, where the water runs out into the bath, the pressure is zero (I'm measuring pressures WRT 1 atmosphere)

If i open the tap little then water runs through it.

There's still a 3 metre head of water, so the pressure is still nearly 3 metres (there's a little pressure drop due to resistance in the pipes, but I can make that as small as I like by using wider bore pipes).

If I open the tap more then the flow increases.

But the pressure drop is still 3 metres.

 

So, quite clearly you are wrong.

The pressure is the same.

It's not going to increase unless you suddenly build another storey on my house so you can move the tank further up.

 

Just in case you are wondering why you have got this so wrong, it may be because you are thinking about the effect of putting a jet on the end of a pupe- for example, by putting your thumb over the end of a hose pipe.

That doesn't increase the flow- it increases the velocity.

[studiot]

Lucid explanation, John. +1

But hydraulics is still a poor to defective analogy for electrics.

Edited November 22, 2015 by studiot

[John Cuthber]

Lucid explanation, John. +1

But hydraulics is still a poor to defective analogy for electrics.

Indeed, it's a lousy analogy.

But, if the guy thinks that increasing the pressure makes less stuff flow (because he can't do basic arithmetic) any analogy will probably work.

[Lagoon Island Pearls]

Indeed, it's a lousy analogy.

But, if the guy thinks that increasing the pressure makes less stuff flow (because he can't do basic arithmetic) any analogy will probably work.

 

I'm not one of the loons that joins here who thinks he's always right and everyone else is wrong.

 

I don't think like that. I can be stood corrected any time when provided with a reasonable explanation. I was only trying to help the OP and I admit to erring.

 

As to Ohms Law, that's the way I was taught. By my father, who was a master electrician. He also would say if you're not sure... think of what water would do. Ohm's law always worked for me when I needed to learn current or resistance. I'm a handy go-to guy among my friends and workmates and can fix most things that are fixable.

 

I didn't feel the need to belittle (no less a scientist), even when I thought I was right. One contributor posted an incorrect assumption about editing after he posted, which if you look at the post times is clearly not true. I didn't read any admonishment there. Snark seems be a pervasive undertone on this board when dealing with people who are actually capable of learning or in this case, relearning something. No doubt that's acceptable if the point is belabored and the OP is intransigent, but it didn't rise to that before getting dismissed as quack. There is a difference.

[John Cuthber]

 

I'm not one of the loons that joins here who thinks he's always right and everyone else is wrong.

 

I don't think like that. I can be stood corrected any time when provided with a reasonable explanation. I was only trying to help the OP and I admit to erring.

 

As to Ohms Law, that's the way I was taught. By my father, who was a master electrician. He also would say if you're not sure... think of what water would do. Ohm's law always worked for me when I needed to learn current or resistance. I'm a handy go-to guy among my friends and workmates and can fix most things that are fixable.

 

I didn't feel the need to belittle (no less a scientist), even when I thought I was right. One contributor posted an incorrect assumption about editing after he posted, which if you look at the post times is clearly not true. I didn't read any admonishment there. Snark seems be a pervasive undertone on this board when dealing with people who are actually capable of learning or in this case, relearning something. No doubt that's acceptable if the point is belabored and the OP is intransigent, but it didn't rise to that before getting dismissed as quack. There is a difference.

"I'm not one of the loons that joins here who thinks he's always right and everyone else is wrong."

So why did you keep insisting you were right when 3 of us were telling you that you were wrong.

 

"No doubt that's acceptable if the point is belabored and the OP is intransigent, "

You did labour it, and you were intransigent.

You started with

"When you use a garden hose, full flow (volume) does not have much effect. Hold your finger over the end (resistance) increases pressure (amps) but reduces volume (volts)."

 

"If you increase the voltage of a circuit, amps drop. If you lower the voltage, amps rise."

 

And again...

"Volts rise with amps? Citation please."

 

and again

"In Ohm's law volts and amps are inversely proportional to resistance".

And again

"As to Ohms Law, that's the way I was taught. "

 

 

So, you saying you are wiling to learn doesn't tally with the evidence.

[Lagoon Island Pearls]

So, you saying you are wiling to learn doesn't tally with the evidence.

 

That means to suggest I'm incapable of learning.

 

I learned two things. 1- I got pressure and volume backasswards and 2- You're a dick.

[John Cuthber]

 

That means to suggest I'm incapable of learning.

 

I learned two things. 1- I got pressure and volume backasswards and 2- You're a dick.

Congratulations on guessing that one of my middle names is Richard, though I don't see how it matters much (it'snot as if I post under my real name here).

 

You also got Ohm's law completely wrong, so it does look like you struggle with learning.

But that's not really the point. Why did you repeatedly post in Ohdearme's thread about ohm's law even though it becae increasingly clear that you don't understand it?

[Lagoon Island Pearls]

Congratulations on guessing that one of my middle names is Richard, though I don't see how it matters much (it'snot as if I post under my real name here).

 

You also got Ohm's law completely wrong, so it does look like you struggle with learning.

But that's not really the point. Why did you repeatedly post in Ohdearme's thread about ohm's law even though it becae increasingly clear that you don't understand it?

 

Because I thought I was right. In retrospect I was wrong. Just because a person gets something wrong doesn't mean they're always wrong.

 

Now you're resorting to fallacies, Dick.

[John Cuthber]

Just because a person gets something wrong doesn't mean they're always wrong.

 

 

It does when they keep repeating it, even after it has been pointed out (by more than one person) that they are wrong.

Every time you say the resistance is inversely proportional to the voltage, you are always wrong.

[Lagoon Island Pearls]

I asked several times to cite the facts. I don't know you and don't accept "wrong" by default unless it's supported.

 

If that's to much to ask on a science board, then you're even a bigger dick than first thought.

[Joatmon]

We seem to be making a meal out of Ohm's law.

Put as simply as I can and assuming other factors like temperature remain constant it applies only to resistance (not inductance or capacitance).

For any resistance in a circuit there will be a voltage across it (V volts)

This voltage will drive a current through it (I amps)

The resistance being considered can be called R ohms.

 

The relationship between V, I and R is constant and usually stated R=V/I ohms.

If you make V the subject of the calculation the formula can be changed to V=I*R volts.

If you make I the subject of the calculation then I= V/R amps.

 

Examples:-

You measure the voltage across a resistor as 20V and you measure the current through it as 2A.The value of that resistor is 20/2 = 10 ohms.

You know you have a resistor of 10 ohms and measure the current through it as 2A . The value of the voltage across it is 2*10 = 20V

You know you have a resistor of 10 ohms and measure the voltage across it as 20V. the value of the current through it is 20/10 = 2A.

 

However, going back to the original question it is unwise and generally of no value to use an ohmmeter in a live circuit which is why R=V/I can be very useful.

Edited November 22, 2015 by Joatmon