## Introduction:

**Fundamental mode**: The low frequency of a periodic waveform is known as the fundamental frequency, which is sometimes alluded to simply as the fundamental. The basic is the musical pitch of a note recognized as the lowest partial present in the music. The fundamental frequency is the minimum intensity sinusoidal in the summation of harmonically linked frequencies, or the frequency of the gap between nearby frequencies, in terms of a superposition of sinusoids. The fundamental is sometimes shortened as f 0, which denotes the lowest frequency when counting from zero. It is most commonly abbreviated as f 1, the first harmonic, in other applications. The second harmonic is f 2 = 2 f 1, and so on.) The zeroth harmonic would’ve been 0 Hz in this case. The ear recognizes the fundamental as the precise tone of the musical tone [harmonic spectrum] since it is the lowest frequency and also heard as the loudest…. Individual partials really aren’t perceived separately; instead, the ear blends them together into a single tone.

**A brief outline:**

**The Mathematical Method: “Initial Sine Curve Condition”**

When you pull each mass element of a stretched string away from the center (flat string) until the string forms the shape of a sine curve, then let go, the entire string vibrates in one normal mode pattern. If you start with a different initial shape, one that isn’t sinusoidal, the string’s motion will be made up of multiple modes.

**The “Feel and Pluck” Method for Musicians**

This is something that guitarists and violinists do all the time. They create a “loop” by softly stroking the string place at a single point (where the node should be) and plucking the string at another position (antinode).

**“Resonance” is a physicist’s method.**

A wave will move to the right (R), hit the fixed end, then reflect back to the left (L) if you gently shake (vibrate) one end of a string up and down (L). If you shake at just the appropriate “resonance” frequency, one that matches one of the string’s natural frequencies, the two travelling waves (R and L) will combine to create a large-amplitude standing wave: STANDING WAVE = R + L

**Important concepts:**

**Standing Wave Equation:**

A new wave pattern is described as a standing wave pattern resulting from the interference of the two waves. Standing waves occur when two waves with the same frequency and amplitude collide while travelling in opposite directions through the same medium.

A wave drifting along the +x direction is reflected at a fixed point. The consequence of its superposition is a standing wave.

**Y _{1} (x, t) = A cos (k x−ωt)**

**Y _{2} (x, t) =−A cos (k x + ωt)**

**y (x, t) =A[cos(k x−ωt) −cos(k x+ωt)]**

**⟹y (x, t) = 2 A sin(k x)sin(ωt)**

**If k x=0, π,2π, …**

**⟹x=0, λ/2, λ,3λ/2, …**

**∴y (x, t) =0**

So, no wave for these points (nodes).

**If k x=π/2,3π/2…**

**⟹x=λ/4,3λ/4, …**

**∴y (x, t) =±2 A cos(ωt)**

**So, these points oscillate by the extreme possible amplitude (antinodes).**

An oscillating system’s **normal mode** is a motion pattern in which all portions of the system flow sinusoidally with the same frequency and phase relation. The normal modes explain free motion that occurs at set frequencies. Natural frequencies, also known as resonant frequencies, are the fixed frequencies of a system’s normal modes. Normal modes and natural frequencies are determined by the structure, materials, and boundary conditions of a physical item, such as a building, bridge, or molecule. Normal modes of vibrating devices (strings, air pipes, drums, and so on) are referred to as “harmonics” or “overtones” in music.

A superposition of a system’s normal modes is its most comprehensive motion. The modes are normal in that they can move separately, which means that stimulation of one mode would never produce motion in another. Normal modes are orthogonal to one another mathematically.

Long-wavelength seismic waves of major earthquakes interfering to produce standing waves generate normal modes in the Earth. Spheroidal, toroidal, and radial (or breathing) modes arise for an elastic, isotropic, homogeneous sphere. Spheroidal modes (like Rayleigh waves) only involve P and SV waves and are dependent on overtone number n and angular order l, but have azimuthal order m degeneracy.

Increasing l brings the fundamental branch closer to the surface, resulting in Rayleigh waves. Toroidal modes are only seen in the fluid outer core and only involve SH waves (like Love waves). Radial modes are simply spheroidal modes with l=0 as a subset. On Earth, the degeneracy doesn’t really exist due to rotation, ellipticity, and 3D heterogeneous velocity.

The self-coupling approximation assumes that each mode may be isolated, while the cross-coupling approximation assumes that numerous modes close in frequency resonate. Self-coupling will only modify the phase velocity of waves around a large circle, not the number of waves, resulting in a stretching or shrinking of the standing wave pattern. Due to the Earth’s rotation, aspherical elastic structure, or ellipticity, modal cross-coupling occurs, resulting in the mixing of underlying spheroidal and toroidal modes.

**Longitudinal waves** are those in which the medium displacement is in the same direction as the wave’s travel direction. The wavelength is the distance here between centres of two consecutive compression or rarefaction areas. Constructive interference occurs the compression and rarefaction zones of two waves coincide, whereas destructive interference occurs whenever the compression and rarefaction areas do not coincide.

Also read: **Degrees of freedom**

**Significance of Fundamental mode in NEET exam:**

The purpose of the **NEET** frequency mode themes is to explain and offer the most likely exam questions. Notes from competent experts in the field, which are accessible on the Infinity Learn free website, can be used to explain them in simple words. If students have a thorough comprehension of the topics covered during the program, multiple-choice questions are designed to practice.

This page on frequency modes covers all of the different types of modes in detail. Examine the thorough notes properly to ensure that you comprehend this topic, as it will aid your preparation for the NEET exam. You can also scribble some brief notes on the longitudinal mode that you can refer to during the exam.

**Frequently asked questions (FAQs):**

**Question 1. What happens if you drop a pebble into a pond full of motionless water?**

**Answer: **When a pebble is put into still water, ripples appear on the surface of the water. These ripples are round in shape and generate alternate crests as they spread out. The kinetic energy of the oscillating particles causes this disruption, and the energy is transmitted to the next layer, generating ripples.

**Question 2. Declare whether the following statements are true or false: Elastic waves are another name for mechanical waves.**

The stated assertion is correct. Because of the elastic nature of the waves, mechanical waves also are known as elastic waves.

**Question 3. Give an example of a situation in which sound waves can pass through gas.**

**Answer**: The required condition for a sound wave to move through the gas is an adiabatic state. This is due to the fact that when sound waves travel, compressions and rarefactions occur, resulting in the formation of heat. As a result, the temperature must remain constant for the waves to travel through the gas. As a result, an adiabatic situation would be optimal.