Calculate 0.100 ohms Resistance of 5.46m Lead Strip

  • Thread starter chris85
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In summary, to get the parallel resistance of a combination of lead and copper of the same area, the copper would need to have a resistivity of 1.72x10^8 and the lead would need a resistivity of 20.6x10^-800.
  • #1
chris85
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Homework Statement

I have a question from an AS level physics paper.Calculate the resistance of a 5.46m length of lead strip,0.450cm wide and 1.25mm thick.What length of similar strip made of copper would have to be put in parallel with the lead strip for the effective resistance of the combination to be 0.100 ohms? (p of Cu and Pb are 1.72x10*-8 and 20.6x10*-800



Homework Equations


I worked the resistance of the lead to be 2 ohms using R+pL/A i know the equation needed is 1/R = 1/r1 + 1/r2 but I am not sure how to find the length of copper needed to get the combine resistance?



The Attempt at a Solution

 
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  • #2
i would post up my working but i don't know how to get all the sighns/symbols up :redface: i have just joined.

Chris.
 
  • #3
Welcome to the PF, chris85. It looks like you are doing all the right things. Just keep using the equation for the resistance of a uniform bar:

[tex]R = \frac{\rho L}{A}[/tex]

and the equation for combining parallel resistances. If the lead is 2 Ohms (I didn't check your math), what resistance do you need to put in parallel to get down to 0.1 Ohms total? And then how long would a copper bar of the same cross-sectional area A have to be to make that resistance?

BTW, there is a LaTex tutorial in the Tutorials forum: https://www.physicsforums.com/showthread.php?t=8997
 
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  • #4
ok well for the resistance of the lead i did

20.6X10^-6 X 5.46M
__________________ = 2.00 ohms so R1 = 1/2 correct?
5.62X10^-7

Now the resistivity of copper is 1.72x10^8 but I'm having trouble finding a value of resistance for the copper that when added to the lead will give a reciprocol 0.1 for the parallel resistance can someone give me a hint where I'm going wrong?
 

FAQ: Calculate 0.100 ohms Resistance of 5.46m Lead Strip

How do I calculate the resistance of a lead strip?

To calculate the resistance of a lead strip, you will need to know its length, cross-sectional area, and resistivity. The formula for resistance is R = ρL/A, where R is resistance, ρ is resistivity, L is length, and A is cross-sectional area. Once you have these values, you can plug them into the formula to calculate the resistance in ohms.

What is the resistivity of lead?

The resistivity of lead is 0.208 microohm-meters. This value may vary slightly depending on the purity of the lead and its temperature. It is important to use the most accurate resistivity value when calculating resistance.

Why is the resistance of the lead strip important?

The resistance of the lead strip is important because it determines how much current can flow through it. High resistance means less current can flow, while low resistance allows for more current to flow. It is also important in determining the power dissipation of the lead strip.

How do I convert meters to millimeters?

To convert meters to millimeters, you can use the conversion factor 1 meter = 1000 millimeters. This means that you will need to multiply the length of your lead strip (in meters) by 1000 to get the length in millimeters. This will ensure that you have the correct units for calculating resistance.

Can resistance be negative?

No, resistance cannot be negative. Resistance is a measure of how much a material opposes the flow of electric current. It is always a positive value, although it can be very small (close to 0) or very large. If you get a negative value when calculating resistance, it is likely due to an error in your calculations or incorrect input values.

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