# student in need of help??

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#### FutureTechn

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

#### jim dungar

##### Moderator
Staff member
What have you tried so far?
Have you tried Ohm's Law?

#### GeorgeB

##### ElectroHydraulics engineer (retired)
To refresh your education, P=E*I. I=E/R. by substitution, P=E*E/R.

Apply those and give us your answer.

Staff member

#### Little Bill

##### Moderator
Staff member
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
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
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.

#### LarryFine

##### Master Electrician Electric Contractor Richmond VA
Otherwise Ohm's law would not apply.
The values don't alter the formula.

#### ATSman

##### ATSman
His definition of power consumption does

#### jim dungar

##### Moderator
Staff member
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
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
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
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.

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#### 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
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
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
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.

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#### kwired

##### Electron manager
I was meaning in general that in parallel circuits the current will differ in general.

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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
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

#### LarryFine

##### Master Electrician Electric Contractor Richmond VA
If two parallel 20 ohm resistors are each burning 10w, what is the voltage across them. Need answer, but also How to solve??
The voltage is the same as that across a single 20-ohm resistor dissipating 10w.

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