# How do I calculate individual dissipated power in a resistor??

#### bsamboy

Joined Dec 8, 2019
5
I need help. I cant figure out this quiz problem even though the answer is there.
I need to see it in expanded form, so I can see the process from the beginning to end

A potential of 135 volts is applied to two resistors connected in parallel. Resistor 1 is 2,700 ohms. Calculate the total power dissipated by Resistor 2 when the total current is 85mA.

The correct answer is: 4.725 watts

#### Papabravo

Joined Feb 24, 2006
14,201
Hint: the current is divided between the two resistors. If you have the voltage across that resistor (135 V) and the value of the resistor (2700 Ω), then how much current is going through that resistor? The rest must be going through the other one.

#### bsamboy

Joined Dec 8, 2019
5
Hint: the current is divided between the two resistors. If you have the voltage across that resistor (135 V) and the value of the resistor (2700 Ω), then how much current is going through that resistor? The rest must be going through the other one.
Hint: the current is divided between the two resistors. If you have the voltage across that resistor (135 V) and the value of the resistor (2700 Ω), then how much current is going through that resistor? The rest must be going through the other one.
Thanks for you simplifying it and helping me to see it was right in front of me the whole time. The book I have only shows the right answer but doesn’t show how to get there.

Thanks again!

#### SteveSh

Joined Nov 5, 2019
105
A slightly different way of looking at this.

You have the total current and voltage, right? From that you can solve for the total resistance of the two resistors in parallel.

If you know the formula for the resistance of 2 resistors in parallel, and you know the value of one of the resistors, 2.7 Kohms in this case, a little algebraic manipulation gives you the value of the other resistor.

#### bsamboy

Joined Dec 8, 2019
5 A slightly different way of looking at this.

You have the total current and voltage, right? From that you can solve for the total resistance of the two resistors in parallel.

If you know the formula for the resistance of 2 resistors in parallel, and you know the value of one of the resistors, 2.7 Kohms in this case, a little algebraic manipulation gives you the value of the other resistor.
The question is how do you come up with 4.725 watts?

#### SteveSh

Joined Nov 5, 2019
105
View attachment 194150

The question is how do you come up with 4.725 watts?
Rt=135V/85mA = 1588 ohms
If R1 = 2700 ohms, then R2 = 3857 ohms.
P=V^2*r = 135^2*3857 ohms = 4.725 W.

MOD: AAC members must limit their posts to only giving guidance and hints, NOT answers, when replying to Homework assignments.

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• bsamboy

#### bsamboy

Joined Dec 8, 2019
5
Rt=135V/85mA = 1588 ohms
If R1 = 2700 ohms, then R2 = 3857 ohms.
P=V^2*r = 135^2*3857 ohms = 4.725 W.
Got it... thanks for breaking it down and building it back up!

#### bsamboy

Joined Dec 8, 2019
5
Rt=135V/85mA = 1588 ohms
If R1 = 2700 ohms, then R2 = 3857 ohms.
P=V^2*r = 135^2*3857 ohms = 4.725 W.

MOD: AAC members must limit their posts to only giving guidance and hints, NOT answers, when replying to Homework assignments.
Sorry, I did not know about getting answers,definitely don't want to break rules of this forum, just wanted to know how they got to that solution of the problem.
Thanks for the help, this forum is great for anyone who wants to know in depth how circuits work

• ericgibbs