Q 11-08-098JEE MainJEE Main 2019 (12 Jan, Shift 2)Easy
A load of mass $M$ kg is suspended from a steel wire of length $2$ m and radius $1.0$ mm in Searle's apparatus experiment. The increase in length produced in the wire is $4.0$ mm. Now the load is fully immersed in a liquid of relative density $2$. The relative density of the material of the load is $8$. The new value of increase in length of the steel wire is:
Answer: (D) $3.0$ mm
Buoyancy is $\dfrac28 = \dfrac14$ of the weight, so the tension becomes $\dfrac34Mg$. Extension is proportional to tension:
$$\Delta l' = \frac34\times4.0 = 3.0\ \text{mm}$$
Solution by Sreeraj P, M.Sc Physics