NEET Physics: Waves – NCERT Masterclass & 100 MCQ Quiz

WAVES

Complete NCERT Study Notes & 5-Part Mega Quiz for NEET

1. Transverse and Longitudinal Waves

Mechanical waves require a material medium (having properties of inertia and elasticity) for their propagation.

• Transverse Waves: Particles of the medium oscillate perpendicular to the direction of wave propagation (e.g., waves on a string, light waves). They can only travel in solids and on the surface of liquids.
• Longitudinal Waves: Particles oscillate parallel to the direction of wave propagation, forming compressions and rarefactions (e.g., sound waves). They can travel in solids, liquids, and gases.

2. Displacement Relation for a Progressive Wave

A harmonic wave traveling in the positive x-direction is represented by:

$$y(x,t) = a \sin(kx - \omega t + \phi)$$

Where $a$ is amplitude, $\omega = 2\pi/T = 2\pi f$ is angular frequency, and $k = 2\pi/\lambda$ is the angular wave number.
Wave velocity $v = \frac{\omega}{k} = f \lambda$.

3. Speed of a Travelling Wave

• Speed of a transverse wave on a stretched string: $v = \sqrt{\frac{T}{\mu}}$ (where $T$ is tension, $\mu$ is linear mass density).
• Speed of a longitudinal wave (sound): Newton originally proposed an isothermal process ($v = \sqrt{P/\rho}$), but Laplace corrected it by proving sound propagation is an adiabatic process: $$v = \sqrt{\frac{\gamma P}{\rho}}$$

Speed of sound is independent of pressure, but directly proportional to the square root of absolute temperature ($v \propto \sqrt{T}$).

4. Superposition of Waves and Standing Waves

When two identical waves traveling in opposite directions superimpose, they form Standing (Stationary) Waves. They do not transfer energy. They consist of Nodes (zero displacement) and Antinodes (maximum displacement).

• String fixed at both ends & Open Organ Pipe: Form all harmonics. Fundamental frequency $f_1 = \frac{v}{2L}$.
• Closed Organ Pipe: Forms only ODD harmonics. Fundamental frequency $f_1 = \frac{v}{4L}$.

5. Phenomenon of Beats

When two sound waves of nearly equal frequencies travel in the same direction, they superimpose to produce periodic variations in the intensity of sound. This waxing and waning of sound is called Beats.

$$\text{Beat Frequency } f_{beat} = |f_1 - f_2|$$

NEET Trick: Waxing a tuning fork decreases its frequency (mass increases). Filing a tuning fork increases its frequency (mass decreases).

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🚀 NEET WAVES MEGA QUIZ (100 MCQ)

Solve the 5 parts below to master Wave Equations, Speed, Interference, and Beats.

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