diffraction gratings: Using the principles of interferences to examine light

Diffraction gratings are used in interference experiments and allow for the separation of light into its constituent wavelengths. This is incredibly useful to analyse light that is being emitted by bodies.
In this video I demonstrate their use, provide the mathematical basis and discuss some applications
Watch and find out
ERRATA: at 8:22 I state 300 line per mm is 3 million lines per meter when in fact its 300,000 lines per meters. the final 'd' value is correct.
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[@donegal79]

Hi Paul d at 9 minutes is 3.3 x 10^-7. Great video as usual, thanks again.

[@PhysicsHigh]

Oh no

[@PhysicsHigh]

thanks for the pick up, though the value is actually correct, The error is stating that 300 line per mm is 3 million line per m, when in fact its 300,000 line per meter. Fortunately the final calculation is correct,

[@essmallgeemuhammadtwahirzu558]

​@@PhysicsHigh Thank you for reception sir. keep the hardwork and editing is important😅

[@Quiskit]

Awesome way of demystifying physics

[@PhysicsHigh]

Thanks

[@whitb62]

Excellent video. Was struggling to understand the difference between diffraction/interference and diffraction grating/double slit.

[@yadiyasin8030]

Omg this man needs to get more famous🤩👌

[@PhysicsHigh]

Thanks. Hope you share and help me on my way 🤓

[@copernicus6420]

What a beautiful explanation

[@Re-nq2uh]

You're a life saver

[@curiousflight5923]

Great explanation.
Thanks ♥️

[@starryx_night]

Great explanation!

[@PhysicsHigh]

Thanks

[@drpindoria]

Very useful observations - thanks for sharing.

[@mrx42]

Brilliant ! Thanks !
Could you please add the uncertainties our yout 'y' and 'd' measurements ? And calculate the propagated uncertainty on the wavelength ? Cheers

[@Hambxne]

brilliant video as usual, i always appreciate your content

[@abyass6]

Very clear explanation, thank you.

[@synth1002]

Best explanation, thanks.

[@naveed3619]

nice explanation , thanks

[@PhysicsHigh]

You’re welcome

[@shamalsawaf8080]

Thank you 💫
It's very useful

[@rabiaassad5489]

Extraordinarily

[@daoudguernazi8644]

thanks a lot :)

[@philipnavin7402]

Awesome!

[@texasfossilguy]

is the 0.14% error due to mfg defects in the grating? temp?

[@SciHeartJourney]

I wish to learn how they manufacture diffraction gratings?

[@ganeshraja1789]

Superb

[@se1toku]

Thanks

[@qigong1001]

So what about non-visible light? How do we calculate infrared wavelengths if we can’t see them? I’m most interested in measuring infrared, thanks.

[@Prof.HaavigPhysics]

For infrared, you need a detector or photopaper that is sensitive to infrared light. Some video cameras with silicon detectors are sensitive to near infrared (you could use one to image the screen on which the IR light is projected from the grating). But do your research. These devices can be expensive. An IR imaging radiometer will work well, but is VERY expensive. You need to know what wavelengths (frequencies) of IR you are dealing with. I assume you have a laser. The company that sells the laser probably also sells alignment detectors that will phosphoresce in visible wavelengths when struck by IR.

[@qigong1001]

@@Prof.HaavigPhysics Thanks. Yes, I researched these IR cards/photopaper. Stuff gets expensive.

[@ARCSTREAMS]

im getting confused with the concept,, when monochromatic beam of light goes through these slits or pin hole is it creating interference fringes due to diffraction and waves colliding with each other? and is the same thing happening with a beam of white light? what is the minimum size that you need for a single slit or pin hole for this to happen? also what happens when light or laser goes through a prism is this dispersion by refraction but there is no interference there?

[@Prof.HaavigPhysics]

Dispersion by refraction occurs because different frequencies of electromagnetic radiation (ie light) move at different velocities through matter, when that matter is transparent to that frequency. There is no interference with a prism.
Interference occurs with diffraction, from a single slit. But diffraction is size dependent. You get the most diffraction when the opening is about the same size as the wavelength. This is true for all waves, not just electromagnetic waves (light). AND there is interference between light from multiple slits, IF that light is of the same frequency and coherent. Coherent means there is a precise relationship between the phases of light passing through each slit. If the light is at random phases, even if it's all the same frequency (like if the light through one slit is from one laser and the light through another slit is from another laser source) you aren't likely to get a recognizable pattern. AND do these frequencies have to be exactly the same? The short answer is yes, but in reality the answer is no, however, the closer the frequency, the more they interfere and the fall-off is very quick! Which leads back to the short answer, that they do need to be the same frequency to interfere. Hope this helps.

[@ARCSTREAMS]

@@Prof.HaavigPhysics kinda thank you for the help , so red laser light passing through diffraction plate will create noticeable interference pattern due to diffraction of coherent freq interfering with each other right? so what happens when a beam of white light is used instead,you still get some kind of rainbow pattern even though there is no coherence in this beam , is diffraction acting differently on both cases? what exactly is diffraction?
"Dispersion by refraction occurs because different frequencies of electromagnetic radiation (ie light) move at different velocities through matte" yeah so what if each freq has a different speed,why would that make the light of a particular freq bend or change direction?

[@Prof.HaavigPhysics]

@@ARCSTREAMS But you DO get coherence with a beam of white light. The beam is from a single source and is therefore self-coherent (the light is in phase with itself, meaning the E-field ripples are all peaking at the same time). When this beam strikes the diffraction plate, the light passing through each slit is the same phase, and will therefore form an interference pattern with the light passing through adjacent slits. But since white light is made up of multiple frequencies (colors), each frequency interferes with the same frequency of light from the other slits, such that, each color of light in the mix forms a separate interference pattern in which the spacing is dependent on the wavelength of that color. Thus the dispersion, resulting in a rainbow effect for each order of the interference pattern.
Diffraction is the curved spreading of waves as they pass through a gap, or around the edges of opaque objects.

[@irisp7858]

"slot antenna" magnetfielt Hz? How get DIY radio wave spectrum?

[@qigong1001]

So if I want to measure just blue wavelength from white light source, can I still measure from m=0 (where it is all white) to m=1(first blue line)? Or do I have to measure from blue to blue? Thanks.

[@Prof.HaavigPhysics]

You measure all of the angles with the triangle formed by the location of the 0th order on the screen, the center of your diffraction grating, and the location of the order of blue light on the screen. The first order is fine, but you can reduce the uncertainty of your angle measurement by measuring the larger angle to the second order blue spot instead of the 1st order spot.

[@qigong1001]

@@Prof.HaavigPhysics ok thanks.

[@kelvinkersey5058]

'I will explain that but first....' and that's when you switch off

[@sahilsharma1985]

Why don't physics teachers use hand held lasers mounted on tripod, compared to large box ones

[@PhysicsHigh]

I could but I wanted something that stayed on continually and my pen lasers were push button only. Also the HeNe laser is AC power based so can run much longer.

[@essmallgeemuhammadtwahirzu558]

Your explanations are great but your data not. there it is supposed to be 3.33 * 10^-7 . numbers are important for application.

[@PhysicsHigh]

I know, and the correction is in the description.

[@KB-lekar]

was about to say this