Wavelength, Frequency and Wave Speed

Terms to describe sound waves: Sound waves can be described by its

1. Wavelength 2. Frequency 3. Time period 4. Amplitude 5. Speed

Amplitude: The maximum displacement of the particles of the medium from their original mean positions on passing a wave through the medium is called amplitude of the wave. It is used to describe the size of the wave. It is usually denoted by the letter A. Its SI unit is metre. The amplitude of a wave is same as the amplitude of the vibrating body producing the wave.

Wavelength: The distance between the two consecutive compressions (C) or two consecutive rarefactions (R) is called the wavelength. Wavelength is the minimum distance in which a sound wave repeats itself. In other words, it is the combined length of a compression and an adjacent rarefaction. It is represented by a Greek letter lambda ‘λ’. Its SI unit is metre (m).

Frequency: The number of complete waves (or oscillations) produced in one second is called frequency of the wave. It is the number of vibrations that occur per second. If we can count the number of the compressions or rarefactions that cross us per unit time, we will get the frequency of sound wave. The frequency of a wave is fixed and does not change even when it passes through different substances. It is denoted by ‘ν’ (Greek letter, nu). Its SI unit is hertz (symbol, Hz) named in honour of Heinrich Rudolf Hertz who discovered photoelectric effect.

Time Period: The time taken by two consecutive compressions or rarefactions to cross a fixed point is called the time period of the wave. In other words, the time required to produce one complete wave (or oscillations) is called time period of the Wave. It is denoted by symbol T. Its SI unit is second (s). The time period of a wave is the reciprocal of its frequency,

$large Time ; Period = frac{1}{Frequency}$

Speed: The distance travelled by a wave in one second is called speed of the wave or velocity of the wave. Under the same physical conditions, the speed of sound remains same for all frequencies. It is represented by letter v. Its SI unit is metre per second (rn/s). Relationship between speed, frequency and wavelength of a wave:

$large Speed = frac{Distance ;travelled}{Time ;taken}$

Sample Questions

(More Questions for each concept available in Login)

Question : 1

A wave of frequency 1000 Hz travels between X and Y, a distance of 600 m in 2 sec. How many wavelengths are there in distance XY?
A. 0.6	B. 1000	C. 180	D. 2000
Right Option : B
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Question : 2

Speed of sound in air at room tempereature is
A. 330 m/s	B. 346 m/s	C. 360 m/s	D. 342 m/s
Right Option : A
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Question : 3

If the change in wavelength of the sound waves is in ratio 2 : 1 then which ratio represents the change in speed of the sound ?
A. 1 : 4	B. 1 : 2	C. 2 : 1	D. 4 : 1
Right Option : C
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