How on earth do you work this wave question out? (phases)

But thats the thing. I don't understand anything that is going on here so I don't know how to describe it.

Also, in the diagram, isn't the dotted line the reflected line. Therefore, if you drew the resultant, then X is the node isn't it, since the two waves cancel eachother out since they are travelling in opposite directions?

no pi radians is 360
pi/2 is 180
pi3/2 is 270
and 1/4pi is 90

oh yeh oh yh..my mistake..

pseudo intellect if i ever saw one

Haven't you done this experiment in class? The waves come out as drawn on that paper.

My physics teacher was dying to show us this in lesson, it's a fun practical as well

All particles between nodes are in phase.

All particles either side of a node are in antiphase.

Because the wave is reflected, the phase is changed by pi radians. So they are now 2pi radians out of phase, which means that they are in phase. Superposition is constructive. The amplitude is now at a maximum, and this is called an antinode.

I don't understand because in between two nodes you get an anti-node, so I don't get how it can be in phase between two nodes. We never did this experiment in class and we probably only had half a lesson on this stuff. It shows a lot too . I don't understand how they become 2pi radians out of phase.

every point between 2 nodes...moves in the same direction

think about a stationary wave..every point between 2 adjacent nodes is moving downwards...and at the same time every point between the nodes next to it are moving upwards

so they are moving in opposite directions..between 2 nodes..ALL points move in the same direction..they are exactly out of phase with every point between the next 2 nodes which are moving upwards

all points between adjacent nodes move in phase
points either side of a node move out of phase

I don't know how I can explain it any better to you

Have you done your exam yet? I suggest you ask your teacher tomorrow

I think I get your first two paragraphs. Are you saying that, as P moves BETWEEN two nodes, by comparing that with when P moves BETWEEN the NEXT two adjacent nodes, they will be out of phase since between the first two nodes, P goes downwards whereas the next two adjacent nodes it is going upwards. The last I understand thanks if I am right in thinking that either side of a node are in anti-phase because one particle moves up whereas another is moving downwards.


In the markscheme it states an answer "Up to node, phase difference is zero/ in phase, beyond node phase difference is pi or in anti-phase."

I don't understand why it could also be zero? Could someone explain that to me?

Also, am I right in thinking that between each adjacent node, it is effectly "pi". Therefore if two particles set of from adjacent nodes in the same direction, they would be "pi" out of phase.

Also, between two adjacent nodes, everything in in phase in the same direction. What would happen if two particles moved in opposite directions from two adjacent nodes?

Like I said many moons ago:

Standing Wave - All points in phase between nodes, all points in antiphase between next two. Amplitude is as it looks on the page.

Progressive Waves - phase differences constantly increases. (until it gets back around to 2pi) Amplitude is constant maximum, even though it may look like its going up and down, that is only because the picture is frozen in time, in a few seconds it will be back up to the max amplitude.