Waves - Result Question 28

28. A wave of frequency $100 Hz$ is sent along a string towards a fixed end. When this wave travels back after reflection, a node is formed at a distance of $10 cm$ from the fixed end of the string. The speeds of incident (and reflected) waves are

[1994]

(a) $5 m / s$

(b) $10 m / s$

(c) $20 m / s$

(d) $40 m / s$

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Answer:

Correct Answer: 28. (c)

Solution:

  1. (c) As fixed end is a node, therefore, distance between two consecutive nodes

$=\frac{\lambda}{2}=10 cm$.

$\lambda=20 cm=0.2 m$

As $v=n \lambda \therefore v=100 \times 0.2=20 m / s$