Ohms law

[Sparky3117]

How do you find source voltage when all you know is resistance?
You have a 5ohm lamp, a 10 ohm lamp, and a 15 ohm lamp. 5 ohms Voltage drop. What is the source voltage?
70
115
208
1100

 

[tom baker]

Hmm that sounds like a test question and a poorly worded one.
Did you make a drawing?

 

[Carultch]

How do you find source voltage when all you know is resistance?
You have a 5ohm lamp, a 10 ohm lamp, and a 15 ohm lamp. 5 ohms Voltage drop. What is the source voltage?
70
115
208
1100

"5 ohms voltage drop" doesn't make sense to me. Perhaps you might want to check the units again.

I recommend sharing your thoughts and method of what you understand so far, so that we can help you the rest of the way. We're glad to help, once we see your input and participation.

 

[Dennis Alwon]

Ohms is ohms not voltage so I agree it makes no sense.

 

[garbo]

Besides what Dennis posted you can never use the room temperature of any incandescent lamp resistance to make any calculations. After a few milliseconds when the filament reaches well over a thousand degrees lamp resistance increases. If a LED lamp had a built in driver you could not use resistance to calculate anything.

 

[JoeStillman]

Ohm's law is an equation with 3 variables. You can't solve the equation unless you know the values of two of the variables. If all you know are ohms, then you can't solve for volts without knowing amps too.

 

[roger]

Is the question asking about a series or parallel circuit?

 

[wwhitney]

Ohm's law is an equation with 3 variables. You can't solve the equation unless you know the values of two of the variables. If all you know are ohms, then you can't solve for volts without knowing amps too.

But if we assume that the OP meant 5 Volts voltage drop on the supply to the lamps, and that the lamps are in parallel, and that the lamp resistances given are their operating resistances, then we have enough information to find the source voltage.

Cheers, Wayne

 

[jim dungar]

But if we assume that the OP meant 5 Volts voltage drop on the supply to the lamps, and that the lamps are in parallel, and that the lamp resistances given are their operating resistances, then we have enough information to find the source voltage.

Cheers, Wayne

Yep.
You just have to choose the "inputs" that equal your desired "output".

Wasn't there a recent meme about this?

 

[JoeStillman]

But if we assume that the OP meant 5 Volts voltage drop ....

There's a definition of "ASSUME" that I just can't shake out of my head.

 

[Jraef]

If ifs and buts were candy and nuts, we'd all have a Merry Christmas

 

[LarryFine]

If ifs and buts were candy and nuts, we'd all have a Merry Christmas

And, "If a frog had wings, he wouldn't bump his ass when he hopped."

 

[ggunn]

And, "If a frog had wings, he wouldn't bump his ass when he hopped."

That was one of my dad's favorite sayings. Another was "How long is a piece of string?"

 

[LarryFine]

That was one of my dad's favorite sayings. Another was "How long is a piece of string?"

To which you say, "No, How Long is a Chinese name."

 

[Jraef]

My Dad’s was:

“You can want in one had and s### in the other, then see which one fills up faster.”

Took me a long time to figure that one out as a kid… I mean, why would you do the second thing at all? Then one day someone told me that they wanted something from me that I was not going to be able to deliver, and the light bulb went off!

 

[LarryFine]