Wavelength Measurement

[Strange]

Just now, John Cuthber said:

I don't understand how this is difficult.

Welcome to the Wonderful World of Dalo where the simplest things are incomprehensible.

[John Cuthber]

1 minute ago, Strange said:

Welcome to the Wonderful World of Dalo where the simplest things are incomprehensible.

That's not a lot more helpful than Dalo's name calling earlier.

[swansont]

13 minutes ago, Dalo said:

 Also, I do not understand how we can use frequency and wavelength in the same equation to calculate the speed of light, when they are transverse to each other.

Frequency*wavelength = speed of the wave

they are inversely related to each other

[Strange]

1 minute ago, John Cuthber said:

That's not a lot more helpful than Dalo's name calling earlier.

Sorry. (A failed attempt at humour.)

[John Cuthber]

It makes a change, I'm usually one of the first to stoop to name calling.

[Dalo]

16 minutes ago, Strange said:

Rays would be sent in all directions from each slit. So, some of those will be parallel but most won't be. (Rays are at right angles to the wavefront so where you have waves going out as concentric circles, the rays will be radial lines.)

Even if they start parallel?

16 minutes ago, Strange said:

Nt sure what you mean by transverse to one another. They are measuring different things. Wavelength is the distance between peaks. Frequency is the rate at which peaks pass some point. So they are obviously related to the speed of the wave.

The wavelength is calculated as the distance between two peaks of the same wave. Let us say on one and the same line as in John's drawing.

Frequency is calculated in the direction in which the wave is moving.

That make them transverse in my view.

13 minutes ago, Strange said:

Wavelength is the distance between the soldiers (distance between peaks).

Speed (of light or whatever) is the speed the soldiers are marching.

Frequency is the rate at which soldiers pass you.

It is what is known as an "analogy".

Then it is a very bad analogy for the model of wavelength as two peaks of the same wave. This would be a perfect analogy for the water wave model which you all have rejected.

 

11 minutes ago, John Cuthber said:

 

I don't understand how this is difficult.

Can you imagine a line of people standing one behind the other?

Can you imagine them all setting off walking?

Can you imagine standing next to that line.

They would walk past you.

If there was a gap of 1 metre between them, and they were walking at 2 metres per second then, in each second, 2 of them would walk past you.

see previous remark.

Edited November 26, 2017 by Dalo

[Strange]

3 minutes ago, Dalo said:

Even if they start parallel?

Yes. That is what happens with diffraction. Each slit acts as a new (almost) omnidirectional source.

4 minutes ago, Dalo said:

The wavelength is calculated as the distance between two peaks of the same wave. Let us say on one and the same line as in John's drawing.

Frequency is calculated in the direction in which the wave is moving.

Well the wave is moving from left to right (say) in that diagram. So if you look at a specific point in the diagram you will see the peaks and troughs moving past. The distance between them is the wavelength. The time between them is the frequency.

6 minutes ago, Dalo said:

Then it is a very bad analogy for the model of wavelength as two peaks of the same wave. This would be a perfect analogy for the water wave model which you all have rejected.

Not sure why you think water waves have been rejected. They have the same properties of wavelength, velocity and frequency.

Does this help:

Wavlength is the distance between any two equivalent points on the waveform.

Speed is how fast the waveform moves from left to right.

Frequency is how fast any red dot goes up and down again (cycles per second or hertz).

[Dalo]

19 minutes ago, Strange said:

Well the wave is moving from left to right (say) in that diagram. So if you look at a specific point in the diagram you will see the peaks and troughs moving past. The distance between them is the wavelength. The time between them is the frequency.

This is, once again, the water wave analogy, where the wavelength is the distance between two consecutive peaks or troughs, in the direction of the wave. And not two peaks or troughs belonging to the same wave (or wavy line in John's drawing)

Edited November 26, 2017 by Dalo

[studiot]

Watching this thread it is immediately obvious that Dalo needs to study the basics of wave motion before he can appreciate the next steps.

What he is attempting to understand is far beyond his present knowledge.

Dalo, in your last thread I gave you a list of things you need to know before you could understand the answer to your question.

You chose not to ask anything about any one of them, so I didn't proceed further.

Here is another shorter list.

The first thing you need to know is the difference between an oscillation, a wave and a sine curve.

Not understanding this trips many people up when they try to study waves.

 

Edited November 26, 2017 by studiot

[Dalo]

1 hour ago, Strange said:

Yes. The frequency is the time between each peak of the wave

Here you make it sound that it is possible to calculate the frequency of peaks on the same wave which are all moving in the same direction at the same time.

Edited November 26, 2017 by Dalo

[John Cuthber]

3 minutes ago, Dalo said:

Here you make it sound that it is possible to calculate the frequency of peaks on the same wave which are all moving in the same direction at the same time.

You can.

[Dalo]

10 minutes ago, studiot said:

Watching this thread it is immediately obvious that Dalo needs to study the basics of wave motion before he can appreciate the next steps.

What he is attempting to understand is far beyond his present knowledge.

Dalo, in your last thread I gave you a list of things you need to know before you could understand the answer to your question.

You chose not to ask anything about one of them.

Here is another shorter list.

The first thing you need to know is the difference between an oscillation, a wave and a sine curve.

Not understanding this trips many people up when they try to study waves.

 

You should not confuse disagreement with misunderstanding. This is a mistake often made in this forum because people are convinced that anybody who understands science perfectly can only agree with it. While it is always possible for people, for me also therefore, to misunderstand things, it should not be considered as automatic. Science thrives on disagreement, more than on consensus.

6 minutes ago, John Cuthber said:

You can.

Of course, but then you would have two frequencies, one in the direction the wave is going, the other along the wave. Is that what you mean?

Edited November 26, 2017 by Dalo

[studiot]

7 minutes ago, Dalo said:

The first thing you need to know is the difference between an oscillation, a wave and a sine curve.

 

So if you know the difference perhaps you can confirm what it is?

 

What is the difference between the frequency of oscillation and the frequency of a wave?

Why does a wave have a wavelength, but an oscillation doesn't

 

 

 

[Dalo]

1 minute ago, studiot said:

 

So if you know the difference perhaps you can confirm what it is?

 

What is the difference between the frequency of oscillation and the frequency of a wave?

Why does a wave have a wavelength, but an oscillation doesn't

 

 

 

You are trying to prove your superiority by testing my knowledge. You would prove it better by answering my questions and showing how I am wrong.

[swansont]

28 minutes ago, Dalo said:

This is, once again, the water wave analogy, where the wavelength is the distance between two consecutive peaks or troughs, in the direction of the wave. And not two peaks or troughs belonging to the same wave (or wavy line in John's drawing)

How is the second sentence in contradiction to the first?

[studiot]

9 minutes ago, Dalo said:

You are trying to prove your superiority by testing my knowledge. You would prove it better by answering my questions and showing how I am wrong.

 

None of this is true.

I am not trying to prove anything.

Either you want help and answers or your don't.

 

You can only base suitable questions on existing knowledge.

The more quickly you come to terms with this the more quickly your will develop your own knowledge and understanding.

 

The differences I mentioned are often not brought out well in physics and other technical courses, so it is a rude awakening for students when they realise that oscillations, waves and sine curves are not the same things.

This was meant to help, not hinder.

 

 

Edited November 26, 2017 by studiot

[Dalo]

7 minutes ago, swansont said:

How is the second sentence in contradiction to the first?

I would certainly not say contradiction. It concerns two different models with different consequences. I do not think they are compatible with each other. Especially, if peaks of the same wave are considered, then the equation (frequency, wavelength, velocity) for the speed of light would not make any sense.

 

3 minutes ago, studiot said:

This was meant to help, not hinder.

That was my initial impression also. It has long vanished.

Edited November 26, 2017 by Dalo

[studiot]

30 minutes ago, Dalo said:

You should not confuse disagreement with misunderstanding. This is a mistake often made in this forum because people are convinced that anybody who understands science perfectly can only agree with it. While it is always possible for people, for me also therefore, to misunderstand things, it should not be considered as automatic. Science thrives on disagreement, more than on consensus.

 

Here is a true story about the Romans, who had conquered everybody and anybody in their path.

Whilst it is true that their superior military resources won through in the end, when they first came to Britain, they nearly lost everything because they rejected simple basic advice form others.

The tides in the Mediterranean are nearly non existant, so they failed to allow for the much higher tides in the Atlantic/North Sea and nearly lost all their boats.

 

It seems to me that you are doing the same.

 

 

Edited November 26, 2017 by studiot

[Dalo]

4 minutes ago, studiot said:

 

Here is a true story about the Romans, who had conquered everybody and anybody in their path.

Whilst it is true that their superior military resources won through in the end, when they first came to Britain, they nearly lost everything because they rejected simple basic advice form others.

The tides in the Mediterranean are nearly non existant, so they failed to allow for the much higher tides in the Atlantic/North Sea and nearly lost all their boats.

 

It seems to me that you are doing the same.

 

 

I think I will keep ignoring you unless you come up with relevant arguments.

Edited November 26, 2017 by Dalo

[studiot]

2 minutes ago, Dalo said:

I think I will keep ignoring you unless you come up with relevant arguments.

Perhaps I should report this post for threats it contains.?

 

I offered you some simple facts, why do you want to hide your head in the sand?

 

And why do you want argument?

 

 

 

 

 

 

 

 

[Strange]

1 hour ago, Dalo said:

This is, once again, the water wave analogy, where the wavelength is the distance between two consecutive peaks or troughs, in the direction of the wave. And not two peaks or troughs belonging to the same wave (or wavy line in John's drawing)

I don't know what you think the difference is. In John's drawing he has marked (with red dots) two consecutive peaks that represent the wavelength. (He has done this for four separate waveforms - not quite sure why, perhaps to show different points in time.)

1 hour ago, Dalo said:

Here you make it sound that it is possible to calculate the frequency of peaks on the same wave which are all moving in the same direction at the same time.

Of course. Why wouldn't it be?

1 hour ago, Dalo said:

Of course, but then you would have two frequencies, one in the direction the wave is going, the other along the wave. Is that what you mean?

There is only one frequency. Look at the animation again. Each red dot is going up and down. They are all doing it at the same frequency (the same number of times per second). They are all at a different phase - a different point along the waveform.

This is also the same time taken for the peaks to pass a fixed point. (In case that is what you mean by "two frequencies")

1 hour ago, Dalo said:

You are trying to prove your superiority by testing my knowledge.

58 minutes ago, Dalo said:

Especially, if peaks of the same wave are considered, then the equation (frequency, wavelength, velocity) for the speed of light would not make any sense.

Why not? 

Edited November 27, 2017 by Strange
"two frequencies"?

[Dalo]

2 minutes ago, Strange said:

I don't know what you think the difference is. In John's drawing he has marked (with red dots) two consecutive peaks that represent the wavelength. (He has done this for four separate waveforms - not quite sure why, perhaps to show different points in time.)

Of course. Why wouldn't it be?

Let me tell you, again, how I understand John's drawing.

If you want to calculate the frequency of a group of waves, you will need at least two waves following each other. The time it takes both waves to cross some line will give you the frequency or periods per second.

You can also consider one wave, and only one, but with more than one peak or trough (a wavy line). This wave, as a whole, moves in a certain direction,  not as it is usually depicted, with its peaks and troughs alternatively crossing a boundary, but as a horizontal line moving vertically.. That is how I understood the claim that the wave length concerns two peaks of the same wave.

I repeatedly said that I had never heard of such a model, and that I did not understand it. But starting with Klaynos, everybody was intent in presenting it as the only reasonable model.

But now, you seem to suggest that there is in fact only one model, and apparently, it is also the model I have always known about.

So, maybe we have been discussing a non-issue? If that is the case, I do not think that I am to blame. Please reread the different posts.

 

[Strange]

Your use of the word "wave" is very confusing.

Quote

If you want to calculate the frequency of a group of waves, you will need at least two waves following each other. The time it takes both waves to cross some line will give you the frequency or periods per second.

By "group of waves" do you mean the sequence of peaks and troughs (sine wave) that makes up the waveforms in John's diagram or my animation? And by "wave" you mean one cycle (peak to peak, say) of that waveform?

Quote

You can also consider one wave, and only one, but with more than one peak or trough (a wavy line). 

But here you use "wave" to mean the whole waveform (many cycles)?

No wonder you are confused...

4 minutes ago, Dalo said:

This wave, as a whole, moves in a certain direction,  not as it is usually depicted, with its peaks and troughs alternatively crossing a boundary, but as a horizontal line moving vertically..

Huh? Not sure where you get that mental model from. See my animation for how wavelength, etc is defined.

 

[swansont]

1 hour ago, Dalo said:

I would certainly not say contradiction. It concerns two different models with different consequences. I do not think they are compatible with each other. Especially, if peaks of the same wave are considered, then the equation (frequency, wavelength, velocity) for the speed of light would not make any sense.

In both descriptions, you're referring to the same wave. How are the descriptions different?

[Dalo]

18 minutes ago, Strange said:

Huh? Not sure where you get that mental model from. See my animation for how wavelength, etc is defined.

Again, reread the posts.

My objection against the concept of wavelength was that it was, to use intuitive terms, in the direction the light is going. But when measuring, it was measured on the screen, which is like a horizontal direction to the vertical direction of the light, or vice versa.

I said that the way wavelength was calculated did not fit with the definition. That is where Klaynos came up with the objection that peaks/troughs belonged to the same wave.

You can now attempt to blame me for my confusing language, but I was not the one creating the confusion. And I still have no answer to my objection.

Edited November 27, 2017 by Dalo