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.
Best Answer
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