Someone help with simple circuit problem?

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Discussion Overview

The discussion revolves around a simple circuit problem involving a series circuit with two resistors (R1 and R2) and a voltage source. Participants explore the calculation of voltage drop across R2, including the use of Ohm's law and the relationship between voltage, current, and resistance.

Discussion Character

  • Homework-related
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant initially calculates the voltage drop across R2 but provides a power value instead, leading to confusion about the correct units.
  • Another participant points out the error in units, emphasizing that watts measure power, not voltage drop, and suggests using Ohm's law to find the current and voltage drops.
  • A later reply provides a step-by-step calculation of the equivalent resistance and the current, ultimately calculating the voltage drop across R2 as 6.43 Volts.
  • One participant expresses gratitude for the correction and information, indicating a willingness to learn and try again.

Areas of Agreement / Disagreement

Participants generally agree on the correct approach to solving the problem using Ohm's law, but there is no explicit consensus on the initial misunderstanding regarding units and calculations.

Contextual Notes

Some assumptions about the circuit configuration and the application of Ohm's law are present, but these are not fully explored or resolved in the discussion.

Who May Find This Useful

Individuals seeking assistance with basic circuit problems, particularly those involving series circuits and Ohm's law, may find this discussion helpful.

ViEternal83
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A series circuit with
R1=5 Ohms
R2=9 Ohms
V=10V

What is voltage drop across R2?

I got 11.11 Watts.

If someone can tell me if I'm wrong or not, it would be much appreciated.

Is this some sort of super smart people's forum where this kind of question is laughed at?
 
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You shouldn't get watts for a voltage drop - watts is power. So your answer is automatically wrong because its incorrect units, and I don't get where you got that number but its wrong.

Few ways to solve this problem, here's one that should be easy to visualize. You know in a series circuit that the current will be identical across the components, so let's find that current and work with that using ohm's law.

Add the series resistance to get the total resistance. You know the voltage, find the current across this total resistance. Now you know the current you can find each voltage drop and both should add to equal your starting voltage.

If you really are looking for power dissapated by R2, its 4.59 watts. I'm not going to simply tell you the voltage drop, show your work and I'm sure someone will help you to learn how to do this yourself, very easy once you get the idea of using ohm's law and this is VERY valuable knowledge.

voltage = current * resistance

Cliff
 
Oh, haha.
I had no idea what I was doing apparently.
But thanks for telling me I was wrong and the information.
I'll try again.
 
Req = R1+R2 = 5 + 9 = 14 Ohms
I = V/Req = 10/14 = 5/7

Voltage drop across R2 = V = I*R2 = 5/7 * 9 = 6.43 Volts
Is this correct?

Thanks for the help.
What a nice forum.
 
Last edited:
Yup, you got it now. Simple algerbra and you can just about figure it all out from ohm's law until you get to AC and non-linear behavior, but that's another story for a different day! :)

Cliff
 

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