# How can 2 waves be in phase if they have different amplitudes?

I feel like I understand it for a second then I lose it again lol
Original post by Gcsestudent56
I feel like I understand it for a second then I lose it again lol

Are these waves in phase? Do they have different amplitudes?

For two waves to be in phase, the only variables that are of concern are its frequency and wavelength. Two waves can only be in phase if they cross the x axis at the same time. The CGP book states the definition of phase as "a measurement of the position of a certain point along the wave cycle." Think about it in terms of circles. When you are drawing a circle of a larger radius, the angle at each point you draw, relative to the origin, is the same as when you are drawing a circle of a smaller radius. So what matters is, are the waves making the same angle relative to a point AT THE SAME TIME.

The amplitude only refers to the energy transferred by the wave. Therefore it makes no difference on waves being in phase. The only exception to this is where you have a "negative" amplitude, which means the energy is being propagated in the opposite direction. You cannot start two waves at both positive and negative values of the same magnitude and call them in phase. In fact they are completely out of phase. This is because the angles they make, relative to a point, are different. They are 180° different. So as waves and circles both have 360° in total for one cycle, just imagine the circle has been cut and positioned into a wave. The points on the circle (and the angle they make with the origin) are the same as the points on the wave. If two circles have the same origin point, but two different radiuses, they are in phase. By this logic, if two waves have the same origin point, but two different amplitudes, they are in phase also. It would help to visualise this by drawing it if you can!

So basically, two waves don't have to be the exact same to be in phase, but they do have to be travelling at the same rate, with the same wavelength, and must have started at the same point along it's cycle.

Hopefully this helps but if you don't get the circle analogy, I don't blame you - it'd a very visual concept and hard to describe on paper. I'd suggest searching for a few yt videos to help visualise this!
Original post by sadfailure

The amplitude only refers to the energy transferred by the wave. Therefore it makes no difference on waves being in phase. The only exception to this is where you have a "negative" amplitude, which means the energy is being propagated in the opposite direction. ...

What is in red and underlined is wrong physics.
Original post by Eimmanuel
What is in red and underlined is wrong physics.

OH NO SORRY! Could you explain please?
I must have been thinking about SMH or smth, would what I said be correct in that case? or is it just completely wrong LMAO
Original post by sadfailure
For two waves to be in phase, the only variables that are of concern are its frequency and wavelength. Two waves can only be in phase if they cross the x axis at the same time. The CGP book states the definition of phase as "a measurement of the position of a certain point along the wave cycle." Think about it in terms of circles. When you are drawing a circle of a larger radius, the angle at each point you draw, relative to the origin, is the same as when you are drawing a circle of a smaller radius. So what matters is, are the waves making the same angle relative to a point AT THE SAME TIME.

The amplitude only refers to the energy transferred by the wave. Therefore it makes no difference on waves being in phase. The only exception to this is where you have a "negative" amplitude, which means the energy is being propagated in the opposite direction. You cannot start two waves at both positive and negative values of the same magnitude and call them in phase. In fact they are completely out of phase. This is because the angles they make, relative to a point, are different. They are 180° different. So as waves and circles both have 360° in total for one cycle, just imagine the circle has been cut and positioned into a wave. The points on the circle (and the angle they make with the origin) are the same as the points on the wave. If two circles have the same origin point, but two different radiuses, they are in phase. By this logic, if two waves have the same origin point, but two different amplitudes, they are in phase also. It would help to visualise this by drawing it if you can!

So basically, two waves don't have to be the exact same to be in phase, but they do have to be travelling at the same rate, with the same wavelength, and must have started at the same point along it's cycle.

Hopefully this helps but if you don't get the circle analogy, I don't blame you - it'd a very visual concept and hard to describe on paper. I'd suggest searching for a few yt videos to help visualise this!

Original post by sadfailure
OH NO SORRY! Could you explain please?

It is noted that energy carried by a wave is related to its amplitude which you mentioned in the beginning of the paragraph.
The negative displacement of the wave has nothing to do with the direction of travel of the wave or the direction of energy transfer.

If you watch the following video for the first 1 minute, you will see that the transverse wave has negative displacement and is travelling from left to right.

I don’t understand what you are trying to explain in your post, to be honest.
Original post by Eimmanuel
It is noted that energy carried by a wave is related to its amplitude which you mentioned in the beginning of the paragraph.
The negative displacement of the wave has nothing to do with the direction of travel of the wave or the direction of energy transfer.
If you watch the following video for the first 1 minute, you will see that the transverse wave has negative displacement and is travelling from left to right.

I don’t understand what you are trying to explain in your post, to be honest.

Oh ok that makes sense! Yeah, sorry all about the confusion (I'm only at A-Level so my knowledge is evidently shaky)!

I was trying to explain a more visual concept, and to be honest it was worded poorly. I was referring more to SHM, as you often see the movement represented by a ball moving around a circle, from birds eye view. And I was also going based off of memory of a Youtube video that I had watched some time ago, but I obviously didn't remember it that well! Again, sorry if my post mislead anyone, I was only trying to help!

Can't wait to understand about waves more in uni though!!