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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

A transverse wave with an amplitude of 0.50 mm and a frequency of...

A transverse wave with an amplitude of 0.50 mm0.50 \text{ mm} and a frequency of 100 Hz100 \text{ Hz} is generated on a wire stretched under a tension of 100 N100 \text{ N}. Given that the wave speed is 100 m s−1100 \text{ m s}^{-1}, determine the average power transmitted to the wire by the source.

Options

  1. A15 mW15 \text{ mW}
  2. B25 mW25 \text{ mW}
  3. C99 mW99 \text{ mW}
  4. D49 mW49 \text{ mW}

Correct answer

D. 49 mW49 \text{ mW}

Step-by-step solution

The average power transmitted by a transverse wave on a stretched string is given by:

Pavg=12μω2A2vP_{avg} = \dfrac{1}{2} \mu \omega^2 A^2 v

The wave speed is related to tension and linear mass density by v=Tμv = \sqrt{\dfrac{T}{\mu}}, which gives μ=Tv2\mu = \dfrac{T}{v^2}.

Substituting μ\mu into the power equation:

Pavg=12(Tv2)ω2A2v=Tω2A22vP_{avg} = \dfrac{1}{2} \left( \dfrac{T}{v^2} \right) \omega^2 A^2 v = \dfrac{T \omega^2 A^2}{2v}

Given values are:
T=100 NT = 100 \text{ N}
v=100 m s−1v = 100 \text{ m s}^{-1}
f=100 Hz⇒ω=2πf=200π rad s−1f = 100 \text{ Hz} \Rightarrow \omega = 2 \pi f = 200 \pi \text{ rad s}^{-1}
A=0.50 mm=0.5×10−3 mA = 0.50 \text{ mm} = 0.5 \times 10^{-3} \text{ m}

Substituting these values:

Pavg=100×(200π)2×(0.5×10−3)22×100P_{avg} = \dfrac{100 \times (200 \pi)^2 \times (0.5 \times 10^{-3})^2}{2 \times 100}

Pavg=12×40000π2×0.25×10−6P_{avg} = \dfrac{1}{2} \times 40000 \pi^2 \times 0.25 \times 10^{-6}

Pavg=5000π2×10−6 WP_{avg} = 5000 \pi^2 \times 10^{-6} \text{ W}

Pavg=5π2×10−3 WP_{avg} = 5 \pi^2 \times 10^{-3} \text{ W}

Using π2≈9.87\pi^2 \approx 9.87:

Pavg≈5×9.87×10−3 W=49.35 mWP_{avg} \approx 5 \times 9.87 \times 10^{-3} \text{ W} = 49.35 \text{ mW}

The closest value is 49 mW49 \text{ mW}.
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