Question

In Searle's apparatus we have two wires. During the experiment we study the extension in one wire. The use of second wire is-
A.to support the apparatus because it is heavy and may not break single wire
B.to compensate the changes in length caused by changes in temperature of atmosphere during experimentation
C.to keep the apparatus in level so that extension is measured accurately
D.all the three above

Answer 1

Hint: Searle's apparatus is an apparatus used as an experiment to measure thermal conductivity of material. It has two wires namely control and test wires which are connected to a horizontal bar at the other ends. During the experiment we concentrate on the test wire to get the results.

Complete answer:
In the experiment to measure thermal conductivity a spirit level is mounted on the horizontal bar, and the bar is hinged to the control wire. Now if we start to increase the weight on the side of the test wire then the test wire gets extended and the spirit level gets tilted by a small amount.
So here we see that the test wire which is playing the important role in the experiment to study the extension in the wire and to get the results and readings but the role of the control wire is not justified in the experiment. So, the role of the control wire is to control the apparatus in a proper position that means the other wire known as control wire keeps the apparatus in the level so that the reading of the tilt of the spirit is taken accurately.
Hence from the above discussion we came to know that the use of a second wire is to keep the apparatus in level so that extension is measured accurately.

So, option (C) is the correct answer.

Note:
With the help of the experiment using Searle's apparatus we can find the young’s modulus of a given material. Young’s modulus of a material is a measure of the elasticity. It is equal to the ratio of the stress acting on a substance or a body or object to the strain produced due to the result of the stress.