Waves and Vibrations

Wave Motion: A periodic disturbance in a medium or space by which energy is transferred from one place to another is called a wave motion.

  

Wave motion is form of disturbance which travels forward through a material medium due to the repeated periodic motion of the particles of the medium about their mean positions, the motion being handed over from one particle to the another particle.

The wave motion is most important means of transmitting energy from one place to another without the transfer of any material medium with it.

 The waves are of two types:

1. Mechanical waves or Elastic waves

2. Non-mechanical waves or Electromagnetic waves

The disturbance may require medium for traveling as in mechanical waves or can travel without the medium i.e. waves can travel through through vacuum  or free space like electromagnetic waves and light waves.

Examples of waves that we use in our daily life for communication and other needs are:

1. Ultrasonic waves for under-sea communication and

2. Detection of cracks in railway lines. 

3. Longitudinal (sound) waves for communication with other people.

4. Light waves for vision.

5. Microwaves are used in mobile communication, defense and other applications.

6. Infrared rays are used in remote areas.

Mechanical Waves: A mechanical wave is a wave that is not capable of transmitting its energy through a vacuum. The existence of medium is essential for propagation. The method of energy propagation in which disturbance propagates with definite velocity without changing its form is called Mechanical Wave.

Mechanical waves are of two types:

1. Transverse Waves

2. Longitudinal Waves.

Wave motion or the traveling waves are also called the progressive waves.

Wave motion represents transfer of energy and not the transfer of the particles of the medium.

Below are the examples that demonstrate the phenomenon of wave motion or progressive wave:

1. Sound Waves : When we speak, the sound waves move outward from us and spread out in every direction without the transfer of any air from us to the listener. 

                                                                                  Similarly if same sound would have been produced on the surface of moon, then the audience would have not received any message because of absence of medium required for the propagation of sound waves on the surface of moon.

                                               

2. Ripples in water : If a stone is thrown in still water, ripples start moving outwards in the form of expanding concentric circles with their centers at the point where the stone was thrown, as shown in fig:

Courtesy: Ducksters

Non-Mechanical Waves or Electromagnetic Waves:The waves which require no material medium for their propagation are called non-mechanical waves or electromagnetic waves. The periodic changes takes place in electric and magnetic fields hence it is called Electromagnetic waves.

Examples :  Light Waves, radio waves, microwaves, X-rays, gamma-rays, thermal radiation  etc.

Properties :

1. In vacuum E.M waves travel with the velocity of light.

2. E.M are transverse in nature and can be polarized.

3. E.M waves have momentum and no material medium is required for their propagation.

Some Multiple Choice Questions:

1. Which of the following is transmitted by a wave ?

     a. Velocity                       b. Displacement
     c. Amplitude                   d. Energy

2. Which of the following waves do not require material medium for their propagation ?

      a. Sound                            b. Light
      c. Ultrasonic                     d. Longitudinal

3. The waves which require medium for propagation are generally known as

      a. Transverse waves            b. Longitudinal waves
      c. Mechanical waves           d. Non-Mechanical waves

4. The waves which do not require medium for their propagation are called

      a. Mechanical waves            b. Electrical waves
      c. Longitudinal waves          d. Non-Mechanical waves

5. Wave motion or the traveling waves are also called

     a. Longitudinal waves           b. Mechanical waves
     c. Non-Mechanical waves     d. Progressive waves

6. A disturbance which travel forwards through a material medium due to repeated periodic motion of the particles of the medium is known as

      a. Energy                               b. Wave
      c. Momentum                        d. Electromagnetic wave

7. The sound waves in air are 

       a. One dimensional                 b. Two dimensional    
       c. Three dimensional              d. None of these

8. The waves on the surface of water in the pond, are 

       a. One dimensional                  b. Two dimensional
       c. Three dimensional               d. None of these

9. Mechanical waves are possible in medium which possesses the poroperty of 

        a. Inertia                                b. Elasticity
        c. both a and b                       d. None of these

10. The essential properties of a medium for the propagation of mechanical waves are

       a. Inertia and Mass                  b. Inertia and Elasticity
       c. Elasticity only                     d. Inertia only


Answers : 
1.  d
2.  b
3.  c
4.  d
5.  d
6.  b
7.  c
8.  b
9.  c
10. b

Coutesy: R.A.Banwat