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**Tips: Calculate actual measurement with scale at different temperature**

In the scenario when the length of scale and object changing with temperature and we have to find correct measurement using the given scale. Use following strategy :

Let Scale gives correct measurement temperature $T$ and we have given scale measurement at $T_{′}$ (say $l_{′}$).

Step 1: Find length of scale at temperature $T$ (Assume $l$).

Step 2: Find change in length of scale $Δl$.

So, Actual measurement of object at temperature $T_{′}$ would be $l_{′}±Δl=l_{′}±(l_{′}−l)$

Now we know the actual length of given object at temperature $T_{′}$.

Using above measurement of object we will find the length of object at all given temperature

A steel scale is correct at $0_{o}C$, the length of a brass tube measured by it at $40_{o}C$ is $5m$. The correct length of the tube at $0_{o}C$ is (Coefficients of linear expansion of steel and brass are $11×10_{−6/_{o}C}$ and $19×10_{−6/_{o}C}$ respectively).