I know that :$$R=\rho\frac{l}{A}$$ where $R$ is the resistance of the wire, $\rho$ is its specific resistance (resistivity), $l$ is its length, and $A$ is the area of cross-section of the wire.

Why do we prefer using materials of high resistivity (like manganin, constantan etc.) in laboratory instruments like potentiometer or Metre Bridge?

I searched everywhere online, but all I always get is the definition of resistivity, which I already know.

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    $\begingroup$ Who said anything about advantages of high resistivity? Physical parameters exist to describe Nature, not only to tell you what's advantageous :) $\endgroup$ – DanielSank Feb 24 '16 at 19:25
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    $\begingroup$ I think this post asks two totally different questions. The first part asks for the general meaning of resistivity. This part you can look up on Wikipedia. The second part asks a good question about lab instrumentation. Why not remove the first part and focus on the second part, which is what you really want to know? $\endgroup$ – DanielSank Feb 24 '16 at 19:27
  • $\begingroup$ @DanielSank That makes sense :) Could you answer that question for me, please? It's really bugging me. $\endgroup$ – agdhruv Feb 24 '16 at 19:39
  • $\begingroup$ As a partial answer to your question, the two materials you mention (manganin, constantan) actually have low resistivities. They are very close to ideal conductors. So laboratory instruments certainly don't use these materials for their high resistivity. $\endgroup$ – David Feb 24 '16 at 20:37
  • $\begingroup$ @ag_dhruv I think Peter's answer is what you need. $\endgroup$ – DanielSank Feb 24 '16 at 21:05

Manganin, like constantin, are alloys invented in the late 1800s to solve a specific problem: resistance varies with temperature, and every resistor passing a current is subject to Joule heating. So if you are building precise electrical metering equipment their is a design advantage to using materials that show a stable resistance with temperature variations.

The follow-on to your question could be: how are precision resistors made? One way is to simply cut strips of high resistance metals to measure; modern surface mount devices use a ceramic core with a metal coating that is laser-trimmed. Carbon film resistors are similar in design, but typically less precise. Or you can grind up the resistance metal and mix it with clay - this gives a resistor that can dissipate heat, and is suitable for high voltage/current applications.

These and more are described here: http://www.learnabout-electronics.org/Resistors/resistors_08.php


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