Wavelength, Frequency and Wave Speed


 
 
Concept Explanation
 

Wavelength, Frequency and Wave Speed

Characteristics of Sound: Sound travels in the form of a wave. Waves are characterized by three basic quantities. They are frequency, speed, and amplitude. Two of the main characteristics of sound are pitch and loudness, which in turn are determined by the frequency and amplitude of the wave, respectively. Therefore, to understand what pitch and loudness mean, we will first need to study the characteristics of waves.

Amplitude:  The maximum displacement of the bob from the mean position during oscillation is called the amplitude of the oscillation. The maximum displacement occurs when the bob is at positions B and C. The position where it comes to stop is called mean position.

                                                           

Time period: When the bob moves from one position and comes back to the same position (moving in the same direction), it is said to complete one oscillation. The time taken to complete one oscillation is called the time period of the oscillation. It is measured in seconds.

Frequency: The number of oscillations per second is called the frequency of oscillation. Faster the vibration of the source, higher is the frequency and higher is the pitch. A pitch sound is called a shrill sound. A low pitch sound is called a hoarse sound.  The, SI unit of frquency is hertz .One hertz is the same as one cycle oer second.

                            dpi{120} fn_jvn large Frequency =frac{No; of; Vibrations; Completed}{Time;Taken} We can say that  

large hertz =frac{1}{second}

Wave speed :  Wave speed can be defined as the distance covered by a wave in one second.

Therefore,

large wave:speed:=:frac{Distance:: Covered }{Time :;Taken }=frac{Wavelength}{Time ;;period}

Relation between wavelength, frequency and wave speed

The region of high density corresponds to compressions, and the region of the low density correspond to rarefraction. At time  large t_1 A is the one of the place where compression is maximum.As time passes, this maximum compression shifts in the direction of propagation of the wave. At time large t_n it reaches C.

Now, the distance AC = distance between consecutive maximum compressions = wavelength large lambda

Also, the time large t_n-t_1 = time period, T.

So, the sound wave moves a distance large lambda in time T. Thus, the wave speed is

                                           large v=lambda /T   

   Here, V denotes wave speed ,  large lambda  denotes wavelength and denotes time taken

As frequency  large v=frac{1}{T}    connecting V and large lambda in terms of the frequency v

V = v large lambda

or, wave speed = frequency large times  wavelength

It hold true for any periodic wave, both for transverse or longitudinal waves.

Sample Questions
(More Questions for each concept available in Login)
Question : 1

A source of wave produces 3 crests and 3 troughs in 0.2 sec, the frequency of the wave is :

Right Option : D
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Question : 2

Doubling the frequency of a sound wave :

Right Option : C
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Question : 3

Two sound waves, having frequencies 2 kHz and 500 Hz respectively, travel towards you. What will be the frequency of the wave that will reach you first ?

Right Option : C
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