# Physics

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#1
So, I have a few questions/confusions:

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1. What's the difference between vibration and oscillation ?

2. There is a definition of the critical angle in my book which says, "It is the largest angle of incidence that a ray in a more optically dense medium can have and still emerge into a less dense medium."

The last (bolded) part confuses me ? Isn't critical angle the angle of incidence for which the angle of refraction becomes 90 degrees ? Which means the refracted ray runs along the boundary and doesn't exactly emerge ???

3. There was a precaution described in my book for the investigation of two-source interference:
"If a strobe light is used to freeze the wave action, people with conditions adversely affected by flashing lights should be warned."

I didn't understand the bolded part. What does that mean ?

4. Also, how does interference occur in a single-slit diffraction even though it's like a one-source thing ?

5. There was this thing written in my book: "CDs have a series of very close lines marked on them and act as a diffraction grating that reflects. This causes the spectrum of colours that can be seen on them from white light that hits the surface."

Explain this, please, it sounds more like a dispersion by prism thing instead, I'm confused

Sinnoh
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Last edited by Missradioactive; 1 year ago
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1 year ago
#2
Oscillation is movement in both up and down motions (like a wave) and a vibration is movement in all directions
1
1 year ago
#3
1. Yeah I think vibration is a more general thing than oscillation, oscillation is mainly used in the context of waves and pendulums.

2. Well, the definitions are kind of equivalent - if you were at the critical angle, and you reduced the angle by an infinitesimal amount, the light would emerge into the less dense medium. But the difference is negligible.

3. If you have a standing wave oscillating at 50Hz, and you're in a dark room, and you flash a light at 50Hz, the wave would appear to be standing still because it would be in the same position every time during the light flash.

4. Some quantum **** (basically, not sure lol)

5. Prisms and diffraction gratings do kind of the same thing if you shine white light on them. If you shine white light at a diffraction grating, because of the many wavelengths of light that compose it, they get diffracted by different angles.
Last edited by Sinnoh; 1 year ago
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#4
(Original post by Sinnoh)
1. Yeah I think vibration is a more general thing than oscillation, oscillation is mainly used in the context of waves and pendulums.

2. Well, the definitions are kind of equivalent - if you were at the critical angle, and you reduced the angle by an infinitesimal amount, the light would emerge into the less dense medium. But the difference is negligible.

3. If you have a standing wave oscillating at 50Hz, and you're in a dark room, and you flash a light at 50Hz, the wave would appear to be standing still because it would be in the same position every time during the light flash.

4. Some quantum **** (basically, not sure lol)

5. Prisms and diffraction gratings do kind of the same thing if you shine white light on them. If you shine white light at a diffraction grating, because of the many wavelengths of light that compose it, they get diffracted by different angles.
Thank you
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#5
(Original post by Sinnoh)
1. Yeah I think vibration is a more general thing than oscillation, oscillation is mainly used in the context of waves and pendulums.

2. Well, the definitions are kind of equivalent - if you were at the critical angle, and you reduced the angle by an infinitesimal amount, the light would emerge into the less dense medium. But the difference is negligible.

3. If you have a standing wave oscillating at 50Hz, and you're in a dark room, and you flash a light at 50Hz, the wave would appear to be standing still because it would be in the same position every time during the light flash.

4. Some quantum **** (basically, not sure lol)

5. Prisms and diffraction gratings do kind of the same thing if you shine white light on them. If you shine white light at a diffraction grating, because of the many wavelengths of light that compose it, they get diffracted by different angles.
Okay, by the way, why exactly a strobe light is used to freeze the wave action ?

And what's the point of doing this in an investigation of two-source interference using a ripple tank ?
Last edited by Missradioactive; 1 year ago
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1 year ago
#6
The single slit can be thought of as a diffraction grating with an asymptotically small slit width. A bit of integration leads to a diffraction pattern as rays of light from one part of the slit interact with rays from other parts of the slit. If you don't know what Huygen's principle is then google it, it makes light a lot more straightforward.

This is not the best diagram but as you can see the light ray to the top of the slit has travelled a bit further so would be out of phase with light with the bottom of the slit, the same is true for eg. a light ray halfway through the slit - it will have some path difference relative to the bottom. If you sum the contributions of the infinite number of rays passing through the slit for a general angle, then you find that there will be a diffraction pattern produced that looks like sin(x) / x
Last edited by username3331778; 1 year ago
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1 year ago
#7
Okay, by the way, why exactly a strobe light is used to freeze the wave action ?

And what's the point of doing this in an investigation of two-source interference using a ripple tank ?
Because it's bright and flashes, I guess. You could use other things, but the idea is that you just see an individual snapshot of the motion of the wave. It also lets you measure wavelengths more easily, because it would appear to the observer that it's frozen in time
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#8
(Original post by Sinnoh)
Because it's bright and flashes, I guess. You could use other things, but the idea is that you just see an individual snapshot of the motion of the wave. It also lets you measure wavelengths more easily, because it would appear to the observer that it's frozen in time
Got it, thank you so much !
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1 year ago
#9
So, I have a few questions/confusions
:...
3. There was a precaution described in my book for the investigation of two-source interference:
"If a strobe light is used to freeze the wave action, people with conditions adversely affected by flashing lights should be warned."
....

If you want to see how strobe light “freeze” wave, have a look at the following video.

The wave is “frozen” at about 0.23 seconds in the video when the strobe light frequency “matches” the frequency of the wave.

Other videos using strobe light:
1
1 year ago
#10
(Original post by Sinnoh)
...
4. Some quantum **** (basically, not sure lol)
...
Diffraction is a wave phenomenon or property NOT quantum behaviour.

I think yolkie had done a good job in explaining the destructive interference in the diffraction of a single slit. A more detail explanation can be found in the following links.

https://opentextbc.ca/physicstestboo...t-diffraction/

https://phys.libretexts.org/Bookshel...it_Diffraction

As for the constructive interference for single slit diffraction, the maths that describes it is more complicated and to my knowledge there is no simple intuitive way of explaining it.

https://sites.ualberta.ca/~pogosyan/...lecture35.html

https://en.wikipedia.org/wiki/Diffra...it_diffraction
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#11
(Original post by Eimmanuel)
Diffraction is a wave phenomenon or property NOT quantum behaviour.

I think yolkie had done a good job in explaining the destructive interference in the diffraction of a single slit. A more detail explanation can be found in the following links.

https://opentextbc.ca/physicstestboo...t-diffraction/

https://phys.libretexts.org/Bookshel...it_Diffraction

As for the constructive interference for single slit diffraction, the maths that describes it is more complicated and to my knowledge there is no simple intuitive way of explaining it.

https://sites.ualberta.ca/~pogosyan/...lecture35.html

https://en.wikipedia.org/wiki/Diffra...it_diffraction
Thank you so much
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