JEE MAIN - Physics (2023 - 10th April Evening Shift - No. 14)

Young's moduli of the material of wires A and B are in the ratio of $$1: 4$$, while its area of cross sections are in the ratio of $$1: 3$$. If the same amount of load is applied to both the wires, the amount of elongation produced in the wires $$\mathrm{A}$$ and $$\mathrm{B}$$ will be in the ratio of

[Assume length of wires A and B are same]

1 : 12
1 : 36
12 : 1
36 : 1

Explanation

Given the formula for elongation in a material due to a force:

$$ \Delta L = \frac{FL}{AY} $$

where:

  • F is the force applied,
  • L is the original length,
  • A is the cross-sectional area of the material, and
  • Y is Young's modulus of the material.

The ratio of the elongations in the two wires A and B is given by:

$$ \frac{\Delta L_1}{\Delta L_2} = \frac{F_1}{F_2} \times \frac{A_2}{A_1} \times \frac{Y_2}{Y_1} $$

Since the same force is applied on both wires (i.e., ($F_1/F_2$ = 1)), the areas are in the ratio 1:3 (i.e., ($A_2/A_1$ = 3)), and the Young's moduli are in the ratio 1:4 (i.e., ($Y_2/Y_1$ = 4)), substituting these values into the equation gives:

$$ \frac{\Delta L_1}{\Delta L_2} = 1 \times 3 \times 4 = 12 $$

So, the ratio of the elongations is 12:1, which indicates that wire A will elongate 12 times more than wire B when the same force is applied.

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