student in need of help??

FutureTechn

New User
Location
cin,oh
Occupation
student
If two parallel 20 ohm resistors are each burning 10w, what is the voltage across them. Need answer, but also How to solve??
 

GeorgeB

ElectroHydraulics engineer (retired)
Location
Greenville SC
Occupation
Retired
To refresh your education, P=E*I. I=E/R. by substitution, P=E*E/R.

Apply those and give us your answer.
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Electrician
If two parallel 20 ohm resistors are each burning 10w, what is the voltage across them. Need answer, but also How to solve??
I will give you one hint.
First solve the resistance for two resisters in parallel.
If you have studied that in parallel circuits, that should be easy to solve.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
1. Welcome to the forum.

2. We don't like to just answer questions, because you don't learn anything; we like to teach how to answer it yourself.

3. All you need to answer it is Ohm's law and "Watt's law": E = I x R and P = E x I.

4. What voltage would cause what current through 20 ohms to expend 10 watts?
 

ATSman

ATSman
Location
San Francisco
Occupation
Self Employed
If two parallel 20 ohm resistors are each burning 10w, what is the voltage across them. Need answer, but also How to solve??
One thing that needs to be clarified is your wording EACH BURNING 10W. When you have 2 resistors in parallel then the 10W power is shared between the two resistors (5W each) because the equivalent circuit value is 10 ohms. Unless you meant that the total circuit wattage is 20W then I stand corrected. Otherwise Ohm's law would not apply.
Yep, the formula P = E squared / R will work to find the voltage.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
It has been more than 24 hours since the question was asked.
This is clearly a homework problem, so without the 'writers' contribution all we are doing is guessing at the actual problem.
 

Another C10

Electrical Contractor 1987 - present
Location
Southern Cal
Occupation
Electrician NEC 2020
Burning is really not the best term to use in electrical, my guess from recollection would be the voltage stays the same , the current will differ.
 

kwired

Electron manager
Location
NE Nebraska
One thing that needs to be clarified is your wording EACH BURNING 10W. When you have 2 resistors in parallel then the 10W power is shared between the two resistors (5W each) because the equivalent circuit value is 10 ohms. Unless you meant that the total circuit wattage is 20W then I stand corrected. Otherwise Ohm's law would not apply.
Yep, the formula P = E squared / R will work to find the voltage.
As worded my first assumption is that the total wattage is 20 watts - 10 ohms per resistor, and that each resistor is 20 ohms. 2 resistors connected in parallel across a voltage source.

This assumes OP did not misunderstand the question and changed critical information when/if it was paraphrased when posted here.
 

pietnel007

Member
Location
Secunda
Parallel circuits, I will assume the voltage across each resistor will be equivalent to to your supply? The current through each one will be different. In a series circuit the voltage over each resistor will differ to the value of resistance and the current will be equal.

Sent from my F8331 using Tapatalk
 

gar

Senior Member
210221-1643 EST

I would reword the question as:

If two 20 ohm resistors are in parallel, and each is dissipating 10w, then what is the voltage across them?

Draw the circuit, look at it closely, and you should easily see how to solve the problem. What is the voltage across a 20 ohm resistor dissipating 10 watts?

.
 

Carultch

Senior Member
Location
Massachusetts
Parallel circuits, I will assume the voltage across each resistor will be equivalent to to your supply? The current through each one will be different. In a series circuit the voltage over each resistor will differ to the value of resistance and the current will be equal.
The current COULD be different, if they were different resistors in parallel. But current will divide equally between the two paths, if both paths have identical resistance.
 

kwired

Electron manager
Location
NE Nebraska
Parallel circuits, I will assume the voltage across each resistor will be equivalent to to your supply? The current through each one will be different. In a series circuit the voltage over each resistor will differ to the value of resistance and the current will be equal.

Sent from my F8331 using Tapatalk
Since they both same Watts and both connected to same voltage then they be the same resistance and each draw same current. (within certain tolerance level anyway)
 

pietnel007

Member
Location
Secunda
Since they both same Watts and both connected to same voltage then they be the same resistance and each draw same current. (within certain tolerance level anyway)
I was meaning in general that in parallel circuits the current will differ in general.

Sent from my F8331 using Tapatalk
 

kwired

Electron manager
Location
NE Nebraska
I was meaning in general that in parallel circuits the current will differ in general.

Sent from my F8331 using Tapatalk
True, because resistance is seldom exactly the same. So it depends on what tolerance level is acceptable before you start to consider those differences.

For basic electricity studies for beginners and a question like this you are generally assuming the resistance of both is identical.

For real world problems and solutions, you have to consider how much tolerance can be accepted for the particular application.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
If I were writing the question, then the resistors would be burning 88.2W each. Or maybe 238.05W.

Then after everyone laughed about the answer we could have a discussion about significant figures.

-Jon
 
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