Question:

A string is stretched between fixed points separated by 75.0 cm. It is observed to have resonant frequencies of 420 Hz and 315 Hz. There are no other resonant frequencies between these two. Then, the lowest resonant frequency for this string is :

Updated On: Jul 5, 2022
  • 105 Hz
  • 1.05 HZ
  • 1050 HZ
  • 10.5 HZ
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The Correct Option is A

Solution and Explanation

For string fixed at both the ends, resonant frequency are given by $f =\frac{n v}{2 L},$where symbols have their usual meanings. It is given that 315 Hz and 420 Hz are two consecutive resonant frequencies, let these are nth and (n + l)th harmonics. $315=\frac{nv}{2L} \, \quad\quad\ldots\left(i\right)$ $420=\frac{\left(n+1\right)v}{2L} \, \quad\ldots$(ii) $=E\left(i\right)+E\left(ii\right) \Rightarrow\frac{315}{420}=\frac{n}{n+1} \Rightarrow n=3$ From E (i), lowest resonant frequency $f _{0}=\frac{v}{2L}=\frac{315}{3}=105 Hz$
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Concepts Used:

Waves

Waves are a disturbance through which the energy travels from one point to another. Most acquainted are surface waves that tour on the water, but sound, mild, and the movement of subatomic particles all exhibit wavelike properties. inside the most effective waves, the disturbance oscillates periodically (see periodic movement) with a set frequency and wavelength.

Types of Waves:

Transverse Waves -

Waves in which the medium moves at right angles to the direction of the wave.

Examples of transverse waves:

  • Water waves (ripples of gravity waves, not sound through water)
  • Light waves
  • S-wave earthquake waves
  • Stringed instruments
  • Torsion wave

The high point of a transverse wave is a crest. The low part is a trough.

Longitudinal Wave -

A longitudinal wave has the movement of the particles in the medium in the same dimension as the direction of movement of the wave.

Examples of longitudinal waves:

  • Sound waves
  • P-type earthquake waves
  • Compression wave