# What is phase difference and how to visualize it?

what is phase difference and how to visualize it?
i can understand it pretty well for sinusoidal waves,but how to visualize it for other type of waves like spherical waves,plane waves etc?

Suraj M
Gold Member
A spherical wave and a plane wave? Are you referring to the shape of the wavefront?

BvU
Homework Helper
A spherical wave and a plane wave? Are you referring to the shape of the wavefront?
yes sir

Check out interference
thank you for replying sir,but i want to know the physical significance of phase angle.like A means the maximum displacement of the particle,time period is the time after which the wave pattern repeats itself and wavelength is the length after which wave pattern repeats itself,so what is the physical significance of phase angle and what does it mean if two waves are in phase or out of phase and how does it change if the wave is not longitudinal ?

Suraj M
Gold Member
I don't think you took gneills advice
You should be able to do a bit of research to find an explanation. Did you try a web search on "string vibration modes"? Do so and take a look at the Hyperphysics web page (Standing Waves on a String) that turns up in the search results.
Try this
https://en.m.wikipedia.org/wiki/Phase_angle

I don't think you took gneills advice

Try this
https://en.m.wikipedia.org/wiki/Phase_angle
sir,i didn't receive gneills comment in my alerts.and i did try many sources including my textbook,reference book,video lectures but all websites treat phase angle only as something that comes in sine wave equation but i don't understand it's physical significance like i do for amplitude A,T,k. these values are independent of wave equation they can be defined without referring to wave equation but why phase angles definition always refer to wave equation?
this is a statement in my textbook"the two spherical sound waves have constant phase difference" how should i visualize this situation?

nasu
Gold Member
If you really understand it for sinusoidal waves, then you should have no problem. The meaning and relevance of the phase angle is the same no matter what is the shape of the wave-fronts or polarization. All these cases (spherical waves versus plane waves, transverse waves versus longitudinal waves) can be sine waves as well.
You may have a problem with understanding this aspect too.

anorlunda
Staff Emeritus
but i want to know the physical significance of phase angle.like A means the maximum displacement of the particle,time period is the time after which the wave pattern repeats itself and wavelength is the length after which wave pattern repeats itself,so what is the physical significance of phase angle and what does it mean if two waves are in phase or out of phase
You're making it harder than necessary. Phase angle has to do with the timing. Two waves are out of phase if they reach maximum displacement at different times. That applies whether or not they are sinusoidal.

davenn
If you really understand it for sinusoidal waves, then you should have no problem. The meaning and relevance of the phase angle is the same no matter what is the shape of the wave-fronts or polarization. All these cases (spherical waves versus plane waves, transverse waves versus longitudinal waves) can be sine waves as well.
You may have a problem with understanding this aspect too.
yes i think i have a problem with that aspect only.i know they can be sine waves as well when you plot a graph between their amplitude or pressure with x and t.does phase angle have no other definition apart from being an angle in sine equation?and you told that spherical waves can also be sinusoidal,and 2 waves are dais to be in phase when
they are like this

how to represent the same when they are spherical ?

You're making it harder than necessary. Phase angle has to do with the timing. Two waves are out of phase if they reach maximum displacement at different times. That applies whether or not they are sinusoidal.
yes sir,i understand but that timing becomes easy to explain when they are sinusoidal like in trasnverse waves but iam unable to understand that timing in longitudinal waves(like spherical waves and plane waves)
please explain that like you explain it to a novice,if possible through a real life example.

anorlunda
Staff Emeritus
yes sir,i understand but that timing becomes easy to explain when they are sinusoidal like in trasnverse waves but iam unable to understand that timing in longitudinal waves(like spherical waves and plane waves)
please explain that like you explain it to a novice,if possible through a real life example.
If you stand in one place and watch on of those other waves go by, you see a sinusoid. Think of the ocean tide. It is a wa e, but measured against a wall at the shore it just goes up and down in a sine wave.

BvU
Homework Helper
The phase angle ##\theta## tells you where you are in the period. So a bit like time, but it jumps back to 0 after one full period.
Does this nice picture help ?

nasu
Gold Member
yes i think i have a problem with that aspect only.i know they can be sine waves as well when you plot a graph between their amplitude or pressure with x and t.does phase angle have no other definition apart from being an angle in sine equation?and you told that spherical waves can also be sinusoidal,and 2 waves are dais to be in phase when
they are like this

how to represent the same when they are spherical ?
I think that now I see where you problem it.
You confound the graph of the displacement versus time with the actual shape of a wave on a string.

The representation of the displacement vesus time for a given point has nothing to with the shape of the wave-fronts or the polarization.
It will look the same for a longitudinal wave.
In a longitudinal wave you represent the longitudinal displacement on the vertical axis versus time on the horizontal axis. The graph will look the same as above.The fact that the displacement is is represented on the vertical axis does not make it transverse. The horizontal axis is time and not the direction of propagation.

I think that now I see where you problem it.
You confound the graph of the displacement versus time with the actual shape of a wave on a string.

The representation of the displacement vesus time for a given point has nothing to with the shape of the wave-fronts or the polarization.
It will look the same for a longitudinal wave.
In a longitudinal wave you represent the longitudinal displacement on the vertical axis versus time on the horizontal axis. The graph will look the same as above.The fact that the displacement is is represented on the vertical axis does not make it transverse. The horizontal axis is time and not the direction of propagation.
so do all waves basically look like sinusoidal waves?
but when you dip 2 fingers in water simultaneously,we can see two spherical waves emerging and they superimpose,how can we say that they are in phase or not?

so don't wavefronts represent the shape of waves and do all waves basically look like sinusoidal waves?
but when you dip 2 fingers in water simultaneously,we can see two spherical waves emerging and they superimpose,how can we say that they are in phase or not?

The phase angle ##\theta## tells you where you are in the period. So a bit like time, but it jumps back to 0 after one full period.
Does this nice picture help ?
yes sir,i understand it well but please explain the same for this exmple,dipping two fingers in water produces spherical waves,now how can we tell that these are in phase or not?since they don't look like sinusoidal

If you stand in one place and watch on of those other waves go by, you see a sinusoid. Think of the ocean tide. It is a wa e, but measured against a wall at the shore it just goes up and down in a sine wave.
yes sir,i understand it well but please explain the same for this exmple,dipping two fingers in water produces spherical waves,now how can we tell that these are in phase or not?since they don't look like sinusoidal

anorlunda
Staff Emeritus
They do look sinusoids like all if you watch them go by one point. One point, not the whole surface.

They do look sinusoids like all if you watch them go by one point. One point, not the whole surface.
what does "look by one point"mean?does it mean we have to look the trajectory of motion of one particle in water?

anorlunda
Staff Emeritus
what does "look by one point"mean?does it mean we have to look the trajectory of motion of one particle in water?
Imagine a pole stuck in the bottom with the top above water. The position of that pole is one point. As the wave passes the pole, the pole sees the water level go up and down sinusoidally. The pole does not see the same wave other places, just that one point.

Imagine a pole stuck in the bottom with the top above water. The position of that pole is one point. As the wave passes the pole, the pole sees the water level go up and down sinusoidally. The pole does not see the same wave other places, just that one point.
so basically are all waves sinusoidal in nature,sound waves,light waves?