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Concepts Of Physics MCQ Edition [Volume 1]
Exam
Concepts Of Physics MCQ Edition [Volume 1]
Subject
Physics
Chapter
Wave Motion and Waves on a String

Concepts Of Physics MCQ Edition [Volume 1] · Physics · Wave Motion and Waves on a String

Two wires A and B , possessing identical geometrical construction,...

Two wires AA and BB, possessing identical geometrical construction, are stretched by a small but equal amount from their natural length. The Young's moduli of the wires are YAY_A and YBY_B while their densities are hoAho_A and hoBho_B. It is given that YA>YBY_A > Y_B and hoA>hoBho_A > ho_B. A transverse signal initiated at one end requires a time t1t_1 to reach the opposite end for wire AA, and t2t_2 for wire BB.

Options

  1. At1>t2t_1 > t_2
  2. Bthe information is insufficient to find the relation between t1t_1 and t2t_2
  3. Ct1<t2t_1 < t_2
  4. Dt1=t2t_1 = t_2

Correct answer

B. the information is insufficient to find the relation between t1t_1 and t2t_2

Step-by-step solution

The speed of a transverse wave on a stretched wire is given by v=Tμv = \sqrt{\dfrac{T}{\mu}}

The tension TT in the wire is T=YAΔLLT = \dfrac{YA \Delta L}{L}

The linear mass density μ\mu is μ=ρA\mu = \rho A

Substituting TT and μ\mu, we get v=YΔLρLv = \sqrt{\dfrac{Y \Delta L}{\rho L}}

The time taken by the transverse signal to travel the length LL is t=Lv=ρL3YΔLt = \dfrac{L}{v} = \sqrt{\dfrac{\rho L^3}{Y \Delta L}}

Since LL and ΔL\Delta L are identical for both wires, t∝ρYt \propto \sqrt{\dfrac{\rho}{Y}}

For wire AA, t1∝ρAYAt_1 \propto \sqrt{\dfrac{\rho_A}{Y_A}} and for wire BB, t2∝ρBYBt_2 \propto \sqrt{\dfrac{\rho_B}{Y_B}}

Given that YA>YBY_A > Y_B and ρA>ρB\rho_A > \rho_B, both the numerator and the denominator for wire AA are greater than those for wire BB. The ratio ρAYA\dfrac{\rho_A}{Y_A} can be greater than, equal to, or less than ρBYB\dfrac{\rho_B}{Y_B}.

Therefore, the given information is insufficient to determine the relation between t1t_1 and t2t_2.
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