Question

Why are alloys and manganen used to make standard resistance?

Answer 1

As we know that Resistance is a property of a material which oppose the electric current to flow through it...
Resistance is simply an oposition to current and the cause of this opposition is Collisions...ie, Collision of charges between the atoms of material or conductor...
More is the Collisions More is the resistance.

It depends on Length , Area , Nature and temperature..

If Temperature of Conductor increases...the thermal motion of charges increases..Due to which they go in random direction and collides with atoms...So increase in temp , increases the collisions as a result Resistance increses too...

But this is not the case for every material...In case of Alloy...Change in temp of an alloy , doesnt affect the Resistance...
This is why we use alloy as standard resistance in lab...