# not understanding how they figure out wave length here

looking at

so from what I understand that is a "standing wave", it's two waves intertwined..

If I count from crest to crest / peak to peak.. I count 9.

And I suppose 9 below too.

And there I might be joining a crest of one wave to a crest of another

Though if I join crest to crest of one wave.. I see maybe 4.5 wave lengths for one of the waves.. and same for the other

But he seems to be counting "loops".. firstly he doesn't define a loop.. I suppose it's either an arc, or a circle? But what has a "loop" got to do with wave length? Is wave length different on a standing wave.. and no longer e.g. crest to crest.. ?

I can see a bit the idea of counting arcs.. 'cos then he at least gets 10.. And then I can see why he'd multiply an result by 2, because there's two waves.

But since when has a wave length been just an arc. So.. i'm quite confused.

Thanks
Original post by gazbo1
looking at

so from what I understand that is a "standing wave", it's two waves intertwined..

Thanks

Standing wave is the result of superposition of two coherent waves travelling in opposite directions. Constructive interference creates antinodes and destructive interference creates nodes.

The distance between two adjacent nodes or antinodes is one half a wavelength. So wavelength in this example is 0.2m
(edited 1 year ago)
Original post by gazbo1
looking at

so from what I understand that is a "standing wave", it's two waves intertwined..

If I count from crest to crest / peak to peak.. I count 9.

And I suppose 9 below too.

And there I might be joining a crest of one wave to a crest of another

Though if I join crest to crest of one wave.. I see maybe 4.5 wave lengths for one of the waves.. and same for the other

But he seems to be counting "loops".. firstly he doesn't define a loop.. I suppose it's either an arc, or a circle? But what has a "loop" got to do with wave length? Is wave length different on a standing wave.. and no longer e.g. crest to crest.. ?

I can see a bit the idea of counting arcs.. 'cos then he at least gets 10.. And then I can see why he'd multiply an result by 2, because there's two waves.

But since when has a wave length been just an arc. So.. i'm quite confused.

Thanks

You need to cover the full distance that the waves are taking up. You can't start after one end and stop before the other end. This means that you will be measuring from the mean position rather than the peak of a wave, but you should be able to see that there are five full waves (or ten half waves) in that space.
ok thanks, I see it much more clearly now.. a standing wave.. so consists of two waves of identical wave length and frequency. And the wave length is 2/10=0.2

The diagram

For me the numbers 1-10 have some use in splitting the length into 10 sections. and one can see that 2/10 i.e. 0.2 of the length, so 0.2M*1M=0.2M is the wave length.

But ,'m a little bit thrown by the term "loop" I get wha the means, visually looking at circles, but Is "loop" a physics term?

I can see the numbers kind of label anti nodes. And I can see benefit to numbering arcs to divide a length in a way to help measure wave length.

And also, the formula he uses

wave length = (total length / number of loops) x 2..

Is that a standard physics formula e.g. as much as V= f λ is?

Thanks
Original post by gazbo1

For me the numbers 1-10 have some use in splitting the length into 10 sections. and one can see that 2/10 i.e. 0.2 of the length, so 0.2M*1M=0.2M is the wave length.

But ,'m a little bit thrown by the term "loop" I get wha the means, visually looking at circles, but Is "loop" a physics term?

I don't think "loop" is a technical physics term, just something that makes sense when compared to the diagram. It's equivalent to "(Total lentgh/Number of half-wavelengths) x 2", or just "Total length/Number of full wavelengths".
Original post by Pangol
I don't think "loop" is a technical physics term, just something that makes sense when compared to the diagram. It's equivalent to "(Total lentgh/Number of half-wavelengths) x 2", or just "Total length/Number of full wavelengths".

Absolutely. There are no 'loops'. Just a string vibrating up and down in a particular pattern.
@gazbo1
The OP might find this link useful - particularly the animations.
http://salfordacoustics.co.uk/sound-waves/standing-waves
(edited 1 year ago)