Coherence and Path Difference - A Level Physics

This video introduces coherence and its relationship with path difference for A Level Physics.

DEFINITION OF COHERENT WAVES IS THAT THEY HAVE A CONSTANT PHASE DIFFERENCE.

Thanks for watching,

Lewis

This video is recommended for anyone studying A Level Physics in the following exam boards:
AQA
CIE
Edexcel
Edexcel IAL
Eduqas
IB
OCR A
OCR B
WJEC

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[mangotangochick]

Just a tip for anyone doing A Level/AS physics:

- The path difference means the 2 waves will not necessarily have the same intensity at a point
- You do get constructive/destructive interference but that does not necessarily mean it is completely constructive/destructive
- Because their amplitudes are not necessarily equal
- This is because I ∝ 1/r² and amplitude depends on the intensity of a wave, since it is dependent on the energy carried by that wave, with one wave carrying less energy because it has travelled further than the other
- So the minimum between 2 maxima is not necessarily going to be 0

This was on my AS last year, and I was so confused about it for ages - it's just because I was so used to thinking all waves had the same amplitude because that's the way we learn about it.

Hope this is helpful :)

[harehnkaundun]

i think u should stress the point that interference happens irrespective of whether the waves are coherent or not. but that Coherence makes the interference observable.

[zhiwaskalimba]

great ..u sorta explained everything my teacher tried to explain for 45 min in 3min..👍

[snowycrystalz]

You should do a series where for each topic you work through some of the really tough exam questions. You are very good at explaining things coherently so I think many of us would benefit!

[PopaDom]

your video is really good, I've been looking for alevel videos for this year and your videos are incredibly simple and comprehensible. Keep up the great work, you'll get more popular in no time with the quality of your videos!

[helloitisiv]

Ohh!your video are so useful! All the knowledge about physical are so easy to understand, thank you !

[usmanalamgir]

These are the best online lectures for physics i have ever found
Thank You very much :)

[RamithHettiarachchi]

Destructive Interference could be (n/2)*λ   - where n= {1, 3, 5, 7...}These videos are great!

[willk]

Constructive interference occurs if each wave is 'in phase', destructive interference occurs when each wave is 'out of phase'. What interference occurs when two waves meet at a point with a phase difference of 90 degrees? the resultant wave has a greater amplitude but yet the wave is not 'in phase'? So I'd say it ought to be constructive interference but the textbooks specify that this only occurs when waves are exactly in phase.

[snowycrystalz]

This video is so so so helpful! Thank you so much!

[PaulEdwardTonkinson]

Shouldn't the condition for destructive interference be (n +1/2) time the wavelength?

[r.b]

Could someone explain how you know the nx value? Is it given?

[ARCSTREAMS]

cant you get coherent light if you pass a regular light source through a pin hole aperture? the waves on the other side will have spatial coherence ? im actually a bit confused about spatial and temporal coherence, , is spatial have to do with the photos all traveling in the same direction and parallel to each other?

[bajranglalkhati]

l understood very
thxx.. for making short but sweet vedios..😊

[saadahmed]

Hi!One question what do you mean by saying "It has got the same color" at 1:16 ??

[seditt]

Can light source be made Coherent if two frequencies which are Harmonics of one another be used if they contain the same phase difference? For instance, Frequency A is 100 hz and Frequency B is 400 hz such that B is the Quarterwave of frequency A so every 4 peaks of B we get a peak of A such that the wave form while being complex is still in perfect phase difference. B would constructively interfer with A once every 4 cycles of B while increasing the overall Energy of the wave to Bf^2 or something along those lines.

[daujisingh]

Sir how to calculate coherence length when we are given two values of wavelengths (x.angstrn to y angstrn).

[AyaanKhan-eigk]

For path difference is it 2n+1 or n+1 lamda/2?

[ElJefe]

So can waves of different wave lengths not interfere?

[danielverrier]

(n/2)y wouldn't work since if n = 2 you would get 1*y you need to use (n+0.5)y. Sorry but I had to use y instead of lander