11. Wave

 

Wave

Waves are movements that carry energy from one place to another without moving matter along with them. There are two main types of waves:

1. 1. Mechanical Waves: These waves need a material medium (like solid, liquid, or gas) to travel through. They're also called elastic waves.

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3. -Longitudinal Waves: When particles in the medium move in the same direction as the wave travels, it's called a longitudinal wave. Examples include waves on a spring or sound waves in the air.

4. -Transverse Waves: When particles in the medium move perpendicular to the direction of the wave, it's called a transverse wave. Examples include waves on a string and waves on the surface of water.

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6. 2. Non-mechanical Waves or Electromagnetic Waves: These waves don't need a medium to travel through and can even move through a vacuum.

7. -Examples include light and heat. All electromagnetic waves, including light and heat, are non-mechanical and consist of particles called photons. The wavelength range of electromagnetic waves is 10^-14 m to 10⁴ m.

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9. -Electromagnetic waves have certain properties:

10. (i) They stay unchanged.

11. (ii) They move in a transverse manner.

12. (iii) They travel at the speed of light.

13. (iv) They carry energy and momentum.

14. (v) The concept of electromagnetic waves was introduced by Maxwell.

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16. However, some waves are not electromagnetic:

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18. (i) Cathode rays (ii) Canal rays (iii) α rays (iv) β rays (v) Sound waves (vi) Ultrasonic waves.

Electromagnetic Waves	Discoverer	Wavelength Range (in meter)	Frequency Range
γ Rays	Henry Becqueral	10-14 to 10-10	1020 to 1018
X-Rays	W. Rontgen	10-10 to 10-8	1018 to 1016
Ultra-violet rays	Ritter	10-8 to 10-7	1016 to 1014
Visible radiation	Newton	3.9 x 10-7 to 7.8 x 10-7	1014 to 1012
Infra-red rays	Hershel	7.8 x 10-7 to 7.8 x 10-3	1012 to 1010
Short radio waves or Hertzian Waves	Heinrich Hertz	10-3 to 1	1010 to 108
Long Radio Waves	Marcony	1 to 104	108 to 106

Note: Electromagnetic waves with a wavelength range of

$10^{-3}$ m to $10^{-2}$ m are called microwaves.

Phase of Vibration: The phase of vibration of a vibrating particle at any instant is the physical quantity that expresses the position as well as the direction of the particle at that instant with respect to its equilibrium (mean) position.

Amplitude: Amplitude is defined as the maximum displacement of the vibrating particle on either side from the equilibrium position.

Wavelength: Wavelength is the distance between any two nearest particles of the medium vibrating in the same phase. It is denoted by the Greek letter lambda ($�$). In a transverse wave, the distance between two consecutive crests or troughs, and in a longitudinal wave, the distance between two consecutive compressions or rarefactions, is equal to the wavelength.

Relation Between Wavelength, Frequency, and Velocity of Wave: The velocity of the wave ($�$) equals the frequency ($�$) multiplied by the wavelength ($�$), expressed as: $�=�\times �$ Or, $�=��$.

A path difference of $\mathrm{\Delta }�$ corresponds to a phase difference $\mathrm{\Delta }�$ where: $\mathrm{\Delta }�=\frac{2�}{�}\cdot \mathrm{\Delta }�$.