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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 are held tight between the same pair of supports. The...

Two wires are held tight between the same pair of supports. The tensions in the wires are in the ratio 2:12 : 1, their radii are in the ratio 3:13 : 1, and their densities are in the ratio 1:21 : 2. Determine the ratio of their fundamental frequencies.

Options

  1. A1:31 : 3
  2. B3:23 : 2
  3. C4:94 : 9
  4. D2:32 : 3

Correct answer

D. 2:32 : 3

Step-by-step solution

The fundamental frequency of a stretched wire is given by:

f=12LTμf = \dfrac{1}{2L} \sqrt{\dfrac{T}{\mu}}

The linear mass density μ\mu can be written in terms of the volume density ρ\rho and radius rr as μ=πr2ρ\mu = \pi r^2 \rho. Substituting this in the frequency formula:

f=12LrTπρf = \dfrac{1}{2Lr} \sqrt{\dfrac{T}{\pi \rho}}

Since both wires are held between the same pair of supports, their lengths LL are equal. The ratio of their fundamental frequencies is:

f1f2=r2r1T1T2×ρ2ρ1\dfrac{f_1}{f_2} = \dfrac{r_2}{r_1} \sqrt{\dfrac{T_1}{T_2} \times \dfrac{\rho_2}{\rho_1}}

Given T1T2=21\dfrac{T_1}{T_2} = \dfrac{2}{1}, r1r2=31\dfrac{r_1}{r_2} = \dfrac{3}{1}, and ρ1ρ2=12\dfrac{\rho_1}{\rho_2} = \dfrac{1}{2}, we substitute these values:

f1f2=1321×21\dfrac{f_1}{f_2} = \dfrac{1}{3} \sqrt{\dfrac{2}{1} \times \dfrac{2}{1}}

f1f2=134=23\dfrac{f_1}{f_2} = \dfrac{1}{3} \sqrt{4} = \dfrac{2}{3}
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