<p>A unit scale is to be prepared whose length does not change with temperature and remains&nbsp; 20cm, using a bimetallic strip made of brass and iron each of different length. The length of both components would change in such a way that difference between their lengths remains constant. If length of brass is 40cm&nbsp; and length of iron will be __________ cm.&nbsp;<span class="equation">\((\alpha_{iron} = 1.2\times10^{-5}K^{-1}\)</span>&nbsp;and&nbsp;<span class="equation">\(\alpha_{brass} = 1.8\times10^{-5}K^{-1}\)</span>)​​​​​​​</p>