Page 310 - General Knowledge

GENERAL KNOWLEDGE 2019

 However, just like UVB, overexposure to UVA has been associated with toughening and
wrinkling of the skin, suppression of the immune system, cataract formation, and skin
cancer.

8. OSCILLATION AND WAVE MOTION
Types of Motion
Periodic Motion
 When a body or a moving particle repeats its motion along a definite path after regular
intervals of time, its motion is said to be Periodic Motion and interval of time is called a time
or harmonic motion period (T).
 The path of periodic motion may be linear, circular, elliptical or any other curve.

Oscillatory motion
 ‗To‘ and Fro' type of motion is called an Oscillatory Motion.
 It need not be periodic and need not have fixed extreme positions.
 The force/torque acting in oscillatory motion (directed towards an equilibrium point) is called
restoring force/torque.

Simple harmonic motion (SHM)
 A particle is said to move in SHM, if its acceleration is proportional to the displacement and
is always directed towards the mean position.
 From our concept of a simple harmonic oscillator we can drive rules for the motion of such a
system.
 We start with our basic force formula,
F = kx.
 Using Newton‘s Second Law, we can substitute for force in terms of acceleration.

Here we have a direct relation between position and acceleration.

Wave motion
 Wave motion is a mode of transmission of energy through a medium in the form of a
disturbance.
 It is due to the repeated periodic motion of the particles of the medium about an equilibrium
position transferring the energy from one particle to another.
 The waves are of three types. They are mechanical, electromagnetic and matter waves.

 Mechanical waves can be produced only in media which possess elasticity and inertia.
 Wave motion is a form of disturbance which travels through a medium due to the repeated
periodic motion of the particles of the medium about their mean position.
 The motion is transferred continuously from one particle to its neighbouring particle.

Characteristics of wave motion
 Wave motion is a form of disturbance travelling in the medium due to the periodic motion of
the particles about their mean position.
 It is necessary that the medium should possess elasticity and inertia.
 All the particles of the medium do not receive the disturbance at the same instant.
 The wave velocity is different from the particle velocity.

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