Notes On Introduction to Waves - CBSE Class 11 Physics
Waves are a series of disturbances which propagate from a source to the surroundings or a destination. They carry along with them a certain amount of energy and information in the form of signals.   Example:   If a pebble is thrown into a pond of still water we see ripples of waves are formed at the place where the pebble touches the surface of water and moving outward in circles. A dry leaf on the surface of the water is seen moving up and down in its place. This shows that the water does not move along with the wave.   This disturbance in the medium that is water, is transmitted from particle to its adjoining particle is due to the elastic forces binding them.   Now let us look at various other examples where waves propagate through other media. In todays’ world that we live in, communication systems play a vital role. These communication systems involve transmission of waves to send and receive information.   For example while communicating through a telephone; the sound waves produced by the vocal cords are converted into electrical waves or signals at the source. These electrical signals can be processed in different ways to reach the receiving end. These electrical signals may be:   Transmitted through a copper cable. Converted into light signals and then transmitted through optical cables Converted into electromagnetic waves and then transmitted through air or communication satellites.   The received signals are converted back to sound waves by the instrument at the receiving end. We have seen that waves travel through various media that is liquid, solid and air. Waves can also travel through vacuum, like sunlight travels through vacuum to reach earth.   Waves are classified into three types, they are: Mechanical waves Electromagnetic waves and Matter waves   Mechanical waves are governed by Newton’s laws and need a medium to propagate, that is solid, liquid or air. Waves in water, sound waves and seismic waves are some examples of mechanical waves.   Examples of mechanical waves: Waves in elastic media that is air, stretched springs, coiled springs etc. are intimately connected with harmonic oscillations which constitute the mechanical waves.   Electromagnetic waves do not require any medium for propagation that is they can travel through vacuum also. They travel with a speed of 299,792,458 m/s which is the speed of light through vacuum.     Examples of Electromagnetic waves:   Visible spectrum, infrared rays, micro – waves, radio waves, ultra violet radiation, X – rays and Gamma radiation are electromagnetic waves.   Matter waves are associated with the moving electrons, protons, neutrons and other fundamental particles. Electron microscope works on the principle of motion of electrons, there by constituting the matter waves.

#### Summary

Waves are a series of disturbances which propagate from a source to the surroundings or a destination. They carry along with them a certain amount of energy and information in the form of signals.   Example:   If a pebble is thrown into a pond of still water we see ripples of waves are formed at the place where the pebble touches the surface of water and moving outward in circles. A dry leaf on the surface of the water is seen moving up and down in its place. This shows that the water does not move along with the wave.   This disturbance in the medium that is water, is transmitted from particle to its adjoining particle is due to the elastic forces binding them.   Now let us look at various other examples where waves propagate through other media. In todays’ world that we live in, communication systems play a vital role. These communication systems involve transmission of waves to send and receive information.   For example while communicating through a telephone; the sound waves produced by the vocal cords are converted into electrical waves or signals at the source. These electrical signals can be processed in different ways to reach the receiving end. These electrical signals may be:   Transmitted through a copper cable. Converted into light signals and then transmitted through optical cables Converted into electromagnetic waves and then transmitted through air or communication satellites.   The received signals are converted back to sound waves by the instrument at the receiving end. We have seen that waves travel through various media that is liquid, solid and air. Waves can also travel through vacuum, like sunlight travels through vacuum to reach earth.   Waves are classified into three types, they are: Mechanical waves Electromagnetic waves and Matter waves   Mechanical waves are governed by Newton’s laws and need a medium to propagate, that is solid, liquid or air. Waves in water, sound waves and seismic waves are some examples of mechanical waves.   Examples of mechanical waves: Waves in elastic media that is air, stretched springs, coiled springs etc. are intimately connected with harmonic oscillations which constitute the mechanical waves.   Electromagnetic waves do not require any medium for propagation that is they can travel through vacuum also. They travel with a speed of 299,792,458 m/s which is the speed of light through vacuum.     Examples of Electromagnetic waves:   Visible spectrum, infrared rays, micro – waves, radio waves, ultra violet radiation, X – rays and Gamma radiation are electromagnetic waves.   Matter waves are associated with the moving electrons, protons, neutrons and other fundamental particles. Electron microscope works on the principle of motion of electrons, there by constituting the matter waves.

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