WAVES AND MOTION CHAPTER NO 12


PHYSICS NOTES 10TH CLASS
Written by BILAL HASAN B.cs , M.cs..
NICE STUDIES ACADEMY HFD
WAVES AND MOTION
BILAL HASAN:BORROWED FEATHERS SELDOM FIT.
WWW.URDULECTURESOFSCIENCE.BLOGSPOT.COM   

DEFINITIONS
1. Vibration


One complete round trip of a simple harmonic motion is called vibration. 
or 
If a body in periodic motion moves to and fro over the same path, this motion is called Oscillation. 
2. Time Period (T)

The time required to complete vibration is known as time period. 
3. Frequency

It is the number of vibrations executed by an oscillating body in one second. 
4. Displacement

It is the distance of a vibrating body at any instant from the equilibrium position. 
5. Amplitude

The maximum distance of the body on either side of its equilibrium position is known as amplitude. 
6. Wave Length

The distance between two consecutive crests and troughs is called wavelength. 

10. Octave

The interval between a waveform and another of twice the frequency is known as Octave. 


Units

Frequency: Cycles per second (eps) or Hertz (hz) 
Wavelength: Meter 
Intensity of Sound: Watt/meter2 or W/m2 
Noise: Decibel (DB) 


Simple Harmonic Motion (S.H.M)

Definition 
"To and fro motion of a body in which acceleration is directly proportional to displacement and always directed towards mean position is known as Simple Harmonic Motion." 

Condition for S.H.M 
The conditions for simple Harmonic Motion are given below: 
Some resisting force must act upon the body.
Acceleration must be directly proportional to the displacement.
Acceleration should be directed towards mean position.
System should be elastic.

Examples 
Following are the examples of S.H.M: 
Body attached to a spring horizontally on an ideal smooth surface.
Motion of a simple and compound pendulum.
Motion of a swing.
Motion of the projection of a body in a circle with uniform circular motion.

Resonance

Definition 
"The large amplitude vibration of an object when given impulses at its natural frequency is known as Resonance." 

Experiment 
Consider a long string stretched tightly between two pegs. Four pendulums A, B, C and D of different lengths are fastened to the string. Another pendulum E of same length as A is also fastened. 
When pendulum E is set to vibrate, it will be observed that all the pendulums start to swing but pendulum A begins to vibrate with larger amplitude, as pendulum E is set into vibration. It imparts its motion to the string. This string in turn imparts the same periodic motion to the pendulums. The natural frequency of all other pendulums except A is different. Due to the same natural frequency only A vibrates as the same vibration of E. This phenomenon under which pendulum A begin to vibrate is called resonance. 

Example 
March of Soldiers while Crossing the Bridge 
Each bridge has its own natural frequency and marching of soldiers is another vibrating system. So there may occur a force on vibration in bridge. This may damage the bridge. So, for safely precautions, it is written that soldiers must march out of stop while crossing the bridge. 


Wave

Definition 
" A method of energy transfer involving some form of vibration is known as a wave." 

Wave Motion 
Wave motion is a form of disturbance, which travels through a medium due to periodic motion of particles of the medium about their mean position. 

Experiment 
We see that if we dip a pencil into a tap of water and take it out a pronounced circular ripple is set up on the water surface and travels towards the edges of the tub. However if we dip the pencil and take it out many times, a number of ripples will be formed one after the other. 
Waves can also be produced on very long ropes. If one end of the rope is fixed and the other end is given sudden up and down jerk, a pulse-shaped wave is formed which travels along the rope. 


Transverse Wave

Definition 
"The wave in which amplitude is perpendicular to the direction of wave motion is known as Transverse Wave." 

Examples 
Radio Waves
Light Waves
Micro Waves
Waves in Water
Waves in String


Longitudinal Wave OR COMPRESSIONAL WAVES

Definition 
"The wave in which amplitude is parallel to wave motion is called longitudinal wave." 

Example 
Sound Waves
Seismic Waves

Difference Between Longitudinal and Transverse Waves

Longitudinal Waves 
1. In longitudinal waves, particles of the medium vibrate in the direction of the waves. 
2. The portion of wave in which particles of medium are very close to each other is called compression. 
3. Examples of longitudinal waves are sound wave and seismic waves. 
4. Distance between the centre of two compressions and rarefactions is called wavelength. 

Transverse Waves 
1. In transverse waves, particles of the medium vibrate in the direction perpendicular to the direction of wave. 
2. The portion in which particles of medium are higher than their normal position is called crest. 
3. Examples of transverse wave are microwaves and radio waves. 
4. Distance between two crests and troughs is called wavelength.






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