## Waves – Class 11 | Chapter – 15 | Physics Short Notes Series PDF for NEET & JEE

Waves: A wave is a disturbance that travels through space and matter, transferring energy from one place to another without the permanent transfer of mass. Waves can exist in various forms and can be characterized by different properties, such as wavelength, frequency, amplitude, velocity, and direction of propagation. The behavior of a wave depends on the medium in which it is traveling, such as solid, liquid, or gas.

There are two main types of waves: mechanical and electromagnetic. Mechanical waves, such as sound waves, require a medium to propagate, while electromagnetic waves, such as light, can travel through a vacuum.

In summary, waves are a common and fundamental phenomenon in physics and play a crucial role in many natural and man-made systems, including communication, energy transfer, and information processing.

## Characteristics of Waves

The characteristics of a wave describe the behavior of a wave and can be used to quantify and compare different types of waves. Some of the most important wave characteristics are:

• Wavelength: The distance between two consecutive peaks or troughs of a wave.
• Frequency: The number of complete wave cycles that pass a fixed point in a given amount of time, usually measured in Hertz (Hz).
• Amplitude: The maximum height of a wave from the equilibrium or rest position.
• Velocity: The speed at which a wave travels through a medium, determined by the wavelength and frequency of the wave.
• Direction of Propagation: The direction in which the wave travels through a medium.
• Phase: The position of a point on the wave relative to its starting point.
• Interference: The interaction of two or more waves that results in the creation of a new wave pattern.
• Diffraction: The bending of waves as they pass through an opening or around an obstacle.
• Reflection: The bouncing back of a wave when it encounters a barrier or change in the medium.
• Refraction: The bending of a wave as it passes from one medium to another with a different velocity.

These wave characteristics play a key role in many natural and man-made systems, including communication, energy transfer, and information processing.

## Formula of Waves

There are many formulas that describe the characteristics and behavior of waves. Some of the most commonly used formulas include:

• Wavelength (λ): λ = v / f, where v is the velocity of the wave and f is the frequency.
• Frequency (f): f = v / λ, where v is the velocity of the wave and λ is the wavelength.
• Velocity (v): v = f × λ, where f is the frequency and λ is the wavelength.
• Wave period (T): T = 1 / f, where f is the frequency.
• Amplitude (A): The amplitude of a wave is a measure of its maximum displacement from the rest position.
• Energy density (u): u = 1/2 × ρ × v2, where ρ is the mass density of th
• e medium and v is the velocity of the wave.
• Power (P): P = A^2 × ρ × v, where A is the amplitude, ρ is the mass density of the medium, and v is the velocity of the wave.
• Intensity (I): I = P / A, where P is the power and A is the amplitude.
• Wave equation: y(x,t) = A × sin(2π(f t – kx)), where y(x,t) is the displacement of the wave at position x and time t, A is the amplitude, f is the frequency, t is the time, k is the wave number, and x is the position.

These formulas provide a mathematical framework for describing and analyzing waves, and can be used to solve a wide range of problems in physics and engineering.

## Waves Formula Derivation

The formulas for waves can be derived using basic principles of physics and mathematics. Here are brief derivations for some of the most common wave formulas:

• Wavelength (λ) and frequency (f) relationship:

The velocity of a wave (v) is given by the product of its wavelength (λ) and frequency (f): v = λf. Solving for λ, we get λ = v / f. And solving for f, we get f = v / λ.

• Wave period (T):

The wave period (T) is the time it takes for a complete wave cycle to pass a fixed point. It is related to the frequency (f) by the formula T = 1 / f.

• Energy density (u):

The energy density (u) of a wave can be calculated from the kinetic energy of the particles in the medium through which the wave is traveling. For a wave with velocity v and mass density ρ, the energy density is given by u = 1/2 × ρ × v^2.

• Power (P):

The power (P) of a wave is the rate at which energy is transmitted through a medium. For a wave with amplitude A, velocity v, and mass density ρ, the power is given by P = A^2 × ρ × v.

• Intensity (I):

The intensity (I) of a wave is a measure of the power per unit area. It is related to the power (P) and amplitude (A) of the wave by the formula I = P / A.

These derivations demonstrate how the basic properties of waves, such as velocity, frequency, amplitude, and mass density, can be combined to calculate other important characteristics of waves, such as wavelength, energy density, power, and intensity.

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