Waves · JEE Preparation Physics

The equation of a standing wave in a string is given by y = 5 sinleft(frac{pi x}{3}right) cos(40pi t), where x and y are in centimeters and t is in s…

Practice question from Waves (JEE Preparation Physics), with the correct answer and a step-by-step solution.

easy · MCQ · Q-702A84

The equation of a standing wave in a string is given by y=5sin⁡(πx3)cos⁡(40πt)y = 5 \sin\left(\frac{\pi x}{3}\right) \cos(40\pi t), where xx and yy are in centimeters and tt is in seconds. What is the distance between two consecutive nodes?

  1. A.3 cm3\text{ cm}Correct answer
  2. B.6 cm6\text{ cm}
  3. C.1.5 cm1.5\text{ cm}
  4. D.12 cm12\text{ cm}

Solution

Comparing the spatial part of the equation with the standard standing wave equation y=Asin⁡(kx)cos⁡(ωt)y = A \sin(kx) \cos(\omega t), we find k=π3k = \frac{\pi}{3}. The wavelength λ\lambda is given by k=2πλk = \frac{2\pi}{\lambda}, so π3=2πλ  ⟹  λ=6 cm\frac{\pi}{3} = \frac{2\pi}{\lambda} \implies \lambda = 6\text{ cm}. The distance between two consecutive nodes is λ2=62=3 cm\frac{\lambda}{2} = \frac{6}{2} = 3\text{ cm}.

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