# The equation of a stationary wave is given by y(x,t) = 2sin πx cos100πt, where x and y are measured in metre and t in second. Calculate the amplitude, wavelength and frequency of component waves whose superposition generated this stationary wave. Also write the equations of component waves.

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by aarzu

2015-04-15T21:35:04+05:30

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Y  (x , t ) =  2  Sin πx    Cos  100π t
x and y are in meters  and t is in seconds.

we use the formula in trigonometry  2 Sin A Cos B = Sin (A+B)  + Sin (A-B)

y (x, t)  =  2  Sin (π x)     Cos (100 π t)
=  Sin (πx + 100πt)    +    Sin  (πx - 100 πt)
=  Sin (πx + 100πt)    -    Sin  (100πt  -  πx )
=  Sin (100 πt + πx)   +  Sin  (100 πt  -  πx + π)

general formula  for a standing wave :  y (x, t) = A Sin (ω t - k x + Ф)

these are the component waves which are part of the stationary wave.

component wave 1:    y1 (x,t)  =  sin (π  x  +  100 π t)
angular frequency = ω    = 100 π  radians/sec
frequency = f  = 50 Hz = ω/2π              Time period: 1/f = 0.02 Sec.
Amplitude = A = 1 m
wave number  k =  - π  rad/meter                       we have formula   ω = k v
velocity  v =  ω / k  = - 100 meters/sec
wavelength λ =  v / f  =  100/50  meters =  2 meters

this component of the wave is traveling in the negative x direction. so its velocity is negative.

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component wave 2:    y1 (x,t)  =  sin ( 100 π t - π x +  π )
angular frequency = ω    = 100 π  radians/sec
frequency = f  = 50 Hz = ω/2π              Time period: 1/f = 0.02 Sec.
Amplitude = A = 1 m
wave number  k =  π  rad/meter                       we have formula   ω = k v
velocity  v =  ω / k  = 100 meters/sec
wavelength λ =  v / f  =  100/50   meters =  2 meters
initial phase angle = π radians

this wave is traveling in the positive x direction.  so  k and v are positive.

But the waves are have a phase difference also.