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Two wires are kept tight between the same pair of supports. The tensions in the wires are in the ratio \(2: 1\), the radii are in the ratio \(3: 1\) and the densities are in the ratio \(1: 2\). Find the ratio of their fundamental frequencies.

Short Answer

Expert verified
The ratio of their fundamental frequencies is 2:3.

Step by step solution

01

Understand the Formula

The fundamental frequency of vibration for a wire is given by the formula \( f = \frac{1}{2L} \sqrt{\frac{T}{\mu}} \), where \( T \) is the tension in the wire, \( L \) is the length of the wire, and \( \mu \) is the linear mass density, which can be expressed as \( \mu = \rho \pi r^2 \). Here, \( \rho \) is the density and \( r \) is the radius of the wire.
02

Express the Given Ratios

The tensions, radii, and densities are given to have the ratios \(2:1\), \(3:1\), and \(1:2\) respectively. Thus, let the tensions be \(2T\) and \(T\), the radii be \(3r\) and \(r\), and the densities be \(\rho\) and \(2\rho\).
03

Calculate the Linear Mass Densities

Using \( \mu = \rho \pi r^2 \), calculate the linear mass density as follows:- For Wire 1: \( \mu_1 = \rho \pi (3r)^2 = 9\rho \pi r^2 \)- For Wire 2: \( \mu_2 = 2\rho \pi r^2 \)
04

Plug Values into Frequency Formula

Use the expression for the fundamental frequency from Step 1:- For Wire 1: \( f_1 = \frac{1}{2L} \sqrt{\frac{2T}{9\rho \pi r^2}} \)- For Wire 2: \( f_2 = \frac{1}{2L} \sqrt{\frac{T}{2\rho \pi r^2}} \)
05

Simplify Each Frequency

Simplify the square root expression for each frequency:- \( f_1 = \frac{1}{2L} \sqrt{\frac{2}{9}} \cdot \sqrt{\frac{T}{\rho \pi r^2}} \)- \( f_2 = \frac{1}{2L} \sqrt{\frac{1}{2}} \cdot \sqrt{\frac{T}{\rho \pi r^2}} \)
06

Find the Ratio of Frequencies

The ratio of the frequencies \( \frac{f_1}{f_2} = \frac{\sqrt{\frac{2}{9}}}{\sqrt{\frac{1}{2}}} \).Simplifying this gives:\[ \frac{f_1}{f_2} = \frac{\sqrt{2}\sqrt{1/2}}{3} = \frac{\sqrt{2}}{3 \cdot \sqrt{1/2}} = \frac{\sqrt{2} \cdot \sqrt{2}}{3 \cdot 2} = \frac{2}{3} \]
07

Conclusion

After simplifying, the ratio of the fundamental frequencies \( f_1 : f_2 \) is \( 2 : 3 \).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Tension in the Wire
Understanding the tension in a wire is critical when studying the fundamental frequency of vibration. Tension, noted as \( T \), is the force applied along the wire, pulling it tight. • The tension directly affects the wave speed on the wire, which in turn influences the frequency.• Higher tension generally leads to higher frequency because the wave traverses the wire faster.
In the original exercise, the tension is given in a ratio of \(2:1\). This means that the tension in the first wire is twice that of the second wire. This difference in tension is a decisive factor when determining the frequency ratio of the two wires.
Linear Mass Density
Linear mass density is another vital concept when analyzing the frequency of a vibrating wire. This density is denoted by \( \mu \) and defined as the mass per unit length of the wire.• It is calculated using the formula \( \mu = \rho \pi r^2 \), where \( \rho \) is the density and \( r \) is the radius.• Linear mass density affects the frequency inversely; higher density tends to lower the frequency because it slows down the wave speed.
In our case, linear mass densities are derived from the given ratios of density and radii. For the first wire, this results in \( 9\rho \pi r^2 \) due to the larger radius, while for the second wire, it’s \( 2\rho \pi r^2 \) with a smaller radius and higher density.
Density Ratio
The density ratio given in the problem helps us understand how material properties of the wire affect the frequency.• Density, \( \rho \), relates to how much mass is in a given volume. It impacts the linear mass density of the wire, which we have seen affects the wave speed and therefore the frequency.
The original conditions present the density ratio as \(1:2\). The first wire has a density \( \rho \) while the second wire has \( 2\rho \). The second wire's higher density contributes to a higher linear mass density, making it vibrate at a lower frequency compared to an identical wire with less density.
Frequency Ratio
The frequency ratio is the ultimate goal of our calculations, providing insight into how different properties interact to affect wave motion.• The formula for frequency \( f = \frac{1}{2L} \sqrt{\frac{T}{\mu}} \) intertwines tension and linear mass density.• The higher the tension and the lower the mass density, the higher the frequency of vibration.In the problem, we derive the frequency ratio by using the given tension and linear mass density ratios. After the detailed math steps, the ratio of fundamental frequencies \( f_1 : f_2 \) results in \( 2 : 3 \). This signifies that the first wire, with higher tension and lower effective density, vibrates at a higher fundamental frequency compared to the second wire.

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Most popular questions from this chapter

A \(2 \cdot 00 \mathrm{~m}\) -long rope, having a mass of \(80 \mathrm{~g}\), is fixed at one end and is tied to a light string at the other end. The tension in the string is \(256 \mathrm{~N}\). (a) Find the frequencies of the fundamental and the first two overtones. (b) Find the wavelength in the fundamental and the first two overtones.

A one-metre long stretched string having a mass of \(40 \mathrm{~g}\) is attached to a tuning fork. The fork vibrates at \(128 \mathrm{~Hz}\) in a direction perpendicular to the string. What should be the tension in the string if it is to vibrate in four loops?

A travelling wave is produced on a long horizontal string by vibrating an end up and down sinusoidally. The amplitude of vibration is \(1 \cdot 0 \mathrm{~cm}\) and the displacement becomes zero 200 times per second. The linear mass density of the string is \(0 \cdot 10 \mathrm{~kg} \mathrm{~m}^{-1}\) and it is kept under a tension of \(90 \mathrm{~N}\). (a) Find the speed and the wavelength of the wave. (b) Assume that the wave moves in the positive \(x\) -direction and at \(t=0\), the end \(x=0\) is at its positive extreme position. Write the wave equation. (c) Find the velocity and acceleration of the particle at \(x=50 \mathrm{~cm}\) at time \(t=10 \mathrm{~ms}\).

Figure (15-E11) shows a string stretched by a block going over a pulley. The string vibrates in its tenth harmonic in unison with a particular tuning fork. When a beaker containing water is brought under the block so that the block is completely dipped into the beaker, the string vibrates in its eleventh harmonic. Find the density of the material of the block.

Figure (15-E10) shows an aluminium wire of length \(60 \mathrm{~cm}\) joined to a steel wire of length \(80 \mathrm{~cm}\) and stretched between two fixed supports. The tension produced is \(40 \mathrm{~N}\). The cross-sectional area of the steel wire is \(1 \cdot 0 \mathrm{~mm}^{2}\) and that of the aluminium wire is \(3 \cdot 0 \mathrm{~mm}^{2}\). What could be the minimum frequency of a tuning fork which can produce standing waves in the system with the joint as a node? The density of aluminium is \(2 \cdot 6 \mathrm{~g} \mathrm{~cm}^{-3}\) and that of steel is \(7 \cdot 8 \mathrm{~g} \mathrm{~cm}^{-3}\).

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