Question

A bimetallic strip is two different metal bars 1 and
2 welded parallel to their length. Given thermal
coefficient of linear expansion , > Q, and length of
bars is same. Upon cooling the strip will bend with
(1) Concave on side 2
(2) Concave on side 1
(3) Convex on side 1
(4) Any of the above is possible​

Answer 1

Answer:

A bimetallic strip is used to convert a temperature change into mechanical displacement. The strip consists of two strips of different metals which expand at different rates as they are heated, usually steel and copper, or in some cases steel and brass. The strips are joined together throughout their length by riveting, brazing or welding. The different expansions force the flat strip to bend one way if heated, and in the opposite direction if cooled below its initial temperature. The metal with the higher coefficient of thermal expansion is on the outer side of the curve when the strip is heated and on the inner side when cooled.

The sideways displacement of the strip is much larger than the small lengthways expansion in either of the two metals. This effect is used in a range of mechanical and electrical devices. In some applications the bimetal strip is used in the flat form. In others, it is wrapped into a coil for compactness. The greater length of the coiled version gives improved sensitivity.

Answer 2

Answer:

The correct answer is option 1,3

Explanation:

The coefficient of linear expansion, $a_{A} > a_{B} .$

Therefore, for the same change in temperature, A will expand or contract more than $B$.

So, when the bi-strip is heated i.e. the temperature is $10^{\circ} \mathrm{C} ,$ bi-strip will bend with $A$ one convex side and B on the concave side.

And when the bi-strip is cooled i.e. temperature decreases more than B. Therefore, $A$ is on the concave side and $B$ is on the convex side.