Question

A typical experimental arrangement to determine the Young's modulus of a material of wire under tension is shown in figure. It consists of two long straight wires of same length and equal radius suspended side by side from a fixed rigid support. The wire $A$ (called the reference wire) carries a millimeter main scale $M$ and a pan to place a weight.

The wire $B$ (called the experimental wire) of uniform area of cross-section also carries a pan in which known weights can be placed, vernier scale is attached to a pointer at the bottom of experimental wire $B$ and main scale is fixed to the reference wire $A$.
With reference to the above description, which of the following statement is correct?
I. The elongation of the wire is measured by the vernier arrangement.
II. The reference wire is used to compensate for any change in lengths.

• A. Only I
• B. Only II
• C. Both I and II
• D. Neither I nor II

Answer 1

Answer: (C)

The weights placed in the pan exert a downward force and stretch the experimental wire under a tensile stress. So, the elongation of the wire (increase in length) is measured by the vernier arrangement.
The reference wire is used to compensate for any change in length that may occur due to change in room temperature, since any change in length of the reference wire due to temperature change will be compensate by an equal change in experimental wire. So, both statements are correct.