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A wave is a disturbance, which propagates energy from
one place to the other without the transportation of
matter.
Waves are broadly of two types:
- Mechanical wave (longitudinal wave and transverse
wave) - Electromagnetic wave
- Following are the electromagnetic (Non-mechanical)
waves-
a. Gama rayas (Highest frequency)
b. X-rays
c. UV rays
d. Visible radiation
e. infra-red rays
f. short radio waves
g. Long radio waves (Lowest frequency)
All are in decreasing order of the frequency
Following waves are not electromagnetic.
a. Cathode rays
b. Canal rays
c. alpha rays
d. beta rays
e. sound wave
f. ultrasonic wave
Longitudinal Waves
- In this wave the particles of the medium vibrate in the
direction of propagation of wave. - Waves on springs or sound waves in air are examples
of longitudinal waves.
Transverse Waves - In this wave, the particles of the medium vibrate
perpendicular to the direction of propagation of wave. - Waves on strings under tension, waves on the surface
of water are the examples of transverse waves.
Electromagnetic Waves - The waves, which do not require medium for their
propagation i.e., which can propagate even through
the vacuum are called electromagnetic waves. - Light radio waves, X-rays etc are the examples of
electromagnetic wave. These waves propagate with
the velocity of light in vacuum.
Sound Waves
Sound waves are longitudinal mechanical waves. Eased on
their frequency range sound waves are divided into
following categories. - The sound waves which lie in the frequency range 20
Hz to 20000 Hz are called audible waves. - The sound waves having frequencies less than 20 Hz
are called infrasonic - The sound waves having frequencies greater than
20000 Hz are called ultrasonic waves. - Ultrasonic waves are used for sending signals,
measuring the depth of see, cleaning clothes and
machinery parts, remaining lamp short from chimney
of factories and in ultrasonography.
Speed of Sound - Speed of sound is maximum in solids minimum in
gases. - When sound goes from one medium to another
medium, its speed and wave length changes, but
frequency remain unchanged. The speed of sound
remains unchanged by the increase or decrease of
pressure. - The speed of sound increases with the increase of
temperature of the medium. - The speed of sound is more in humid air than in dry
air because the density of humid air is less than the
density.
Echo: The repetition of sound due to reflection of sound
waves is called an echo.
Intensity: It is defined as amount of energy passing
normally per unit area held around that point per source
unit time.
Pitch: The sensation of a frequency is commonly referred
to as the pitch of a sound.
Sonar: It stands for sound navigation and ranging. It is
used to measure the depth of a sea, to locate the enemy
submarines and shipwrecks.
Doppler’s Effect
If there is a relative motion between source of sound and
observer, the apparent frequency of sound heard by the
observer is different from the actual frequency of sound
emitted by the source. 1 his phenomenon is called
Doppler’s Effect