A copper wire and an iron wire - Potential difference

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Homework Help Overview

The problem involves a copper wire and an iron wire of equal length and diameter, connected in series with a potential difference applied across them. The task is to determine the potential difference across the iron wire given specific values for length, diameter, and total voltage.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss the derivation of the equations used in the solution attempt and question their origins. There is a focus on understanding the relationship between resistance and potential difference, as well as the application of Ohm's law.

Discussion Status

Some participants have provided insights into the equations and concepts involved, such as Ohm's law and the potential relevance of Kirchhoff's Voltage Law. There is an ongoing exploration of the necessary calculations and the need for additional information regarding the conductivities of the materials involved.

Contextual Notes

Participants note that the problem may precede the introduction of certain concepts in their coursework, leading to questions about the appropriateness of the exercise's placement. There is also mention of missing information regarding the conductivities of copper and iron, which are essential for the calculations.

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Homework Statement


A copper wire and an iron wire of equal length l and diameter d are joined, and a potential difference V is applied between the ends of the composite wire. Calculate the potential difference (in volts) across the iron wire. Assume that l = 2.00 m., d = 0.30 mm., and V = 156 V.

The Attempt at a Solution



156 * 10 / (10+1.7) = 133.33 volts

156 * 1.7 / (10+1.7) = 22.67 volts

My question is: where do these equations come from? What are the derivations?

Thanks in advance.
 
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How did you come up with with your solution attempt and what are your thoughts behind it ?
 
I should have noted that the solution and question in and of itself I found while searching google. I just want to know how they came about this solution i.e. where did this equation come from.
 
Ah... I think its a remix of Ohm law, V=RI , where they have rewritten the resistance as L/(σ*A) , where σ is the conductivity of a given material.

I not entirely sure tho, some units on the calculations would have helped a lot hehe
 
Lazar Lakic said:
I not entirely sure tho, some units on the calculations would have helped a lot hehe

Yea exactly what I thought. In general it is: ##\Delta V_1 = \frac{\Delta V * R_1}{R_1+R_2}##. I tried to work backwards having the denominator on the other side but still not sure what it could be. I then thought it has something to do with resistors in parallel but this exercise comes from a chapter before DC circuits are introduced.
 
On the right track , try to Calculate Rcopper and RIron and the current separately.
I think you are supposed to find the conductivity of Iron and copper in your book as they are not stated in the problem.
 

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