small physics doubts (1 Viewer)

[john-doe]

is there any difference between reflecting and emitting?? having difficulty understanding quantum theory...

also, i watched this video on youtube where this guy pours liquid nitrogen on an object and puts a magnet above it, it keeps levitating! how can this happen? this can only happen when both of them are magnets, one of them is a magnet but the other one is just something surrounded by liquid nitrogen. For it to become a magnet it must be passed through a current, but this is not shown??

does that mean if i pour liquid nitrogen to anything, it will become a magnet??? These small things bother me a lot!

 

[nightweaver066]

What exactly are you finding difficult to understand about quantum theory?

Reflecting is to throw back without absorbing (how light bounces off a mirror) where as emitting is to produce and discharge.

The phenomena you observed involving magnets, superconductors and liquid nitrogen is due to the Meissner effect.
The Meissner effect is how superconductors below their critical temperatures expel all magnetic field lines.
This occurs when a superconductor (can either be metal [Type I] or ceramic [Type II]) is cooled below its critical temperature (using liquid nitrogen).

So when a magnet is placed above a superconductor, by Faraday & Lenz' law, persistent currents are produced within the superconductor which oppose the change in magnetic flux.
This produces an equal and opposite magnetic flux, resulting in an equal and opposite force pushing the magnet up balancing the weight force and so the magnet levitates.

 

[john-doe]

What exactly are you finding difficult to understand about quantum theory?

how is light a particle and a wave??

 

[nightweaver066]

how is light a particle and a wave??

It's not a particle and a wave. It behaves as a particle or a wave. There are no experiments where light exhibits both particle and wave properties simultaneously.

Light must be considered as a particle to explain certain phenomena such as black body radiation and the photoelectric effect.

We also know that light behaves as a wave as it can undergo diffraction, reflection, refraction etc.

 

[scarvesss]

how is light a particle and a wave??

qualities of wave:
- diffract
- reflect
- refract

qualities of particle
- thomsons charge to mass ratio experiment showed light was of charged particle nature as mag + elec field deflected/attracted the light
- the paddle wheel experiment
- photoelectric effect

light has dual nature of wave and particle, hence wave-particle duality. that is pretty important.

 

[nightweaver066]

qualities of wave:
- diffract
- reflect
- refract

qualities of particle
- thomsons charge to mass ratio experiment showed light was of charged particle nature as mag + elec field deflected/attracted the light
- the paddle wheel experiment
- photoelectric effect

light has dual nature of wave and particle, hence wave-particle duality. that is pretty important, and if you dont know it by this stage id be a little worried.

*cough cathode rays

 

[john-doe]

- thomsons charge to mass ratio experiment showed light was of charged particle nature as mag + elec field deflected/attracted the light
- the paddle wheel experiment
.

those were cathode rays! i think they are different than light???

also do u guys have sets of "skills" questions from photoelectric effect topic...i have an assessment on it tomorrow?

 

[scarvesss]

*cough cathode rays

did that not show there was particle nature? i was taught it does.

 

[nightweaver066]

did that not show there was particle nature? i was taught it does.

That was to do with the debate whether cathode rays (streams of electrons produced in discharge tubes) were waves/particles.

 

[nightweaver066]

those were cathode rays! i think they are different than light???

also do u guys have sets of "skills" questions from photoelectric effect topic...i have an assessment on it tomorrow?

Sorry i don't, but go through a textbook and past HSC/trial papers for questions on it.

 

[scarvesss]

That was to do with the debate whether cathode rays (streams of electrons produced in discharge tubes) were waves/particles.

i was taught that those experiments were like the first evidence that pointed towards particle nature. i wrote this in trials and i got full marks for the question, so im going with what i know.

 

[nightweaver066]

i was taught that those experiments were like the first evidence that pointed towards particle nature. i wrote this in trials and i got full marks for the question, so im going with what i know.

Okay.. but i suggest you read over that section in a textbook.

 

[scarvesss]

Okay.. but i suggest you read over that section in a textbook.

will do

 

[Parvee]

Okay.. but i suggest you read over that section in a textbook.

^

 

[someth1ng]

i was taught that those experiments were like the first evidence that pointed towards particle nature. i wrote this in trials and i got full marks for the question, so im going with what i know.

If that's the case, you were not deserving of full marks. Those experiments were only to distinguish cathode rays as either waves or particles, NOT light.

Evidence for CR as a wave:
Cathode rays could pass through thin metal foils suggesting that it was a wave.
Cathode rays could produce a shadow (straight lines) showing it was a wave.

Evidence for CR as a particle:
Cathode rays could push a paddle wheel upwards against gravity.
Cathode rays travelled significantly slower than light.
Cathode rays could be deflected in electric/magnetic fields by RH rule (charged)
Cathode rays left the cathode at 90 degrees, unlike light normally emitted from a black body in all directions.

 

[barbernator]

qualities of wave:
- diffract
- reflect
- refract

qualities of particle
- thomsons charge to mass ratio experiment showed light was of charged particle nature as mag + elec field deflected/attracted the light
- the paddle wheel experiment
- photoelectric effect

light has dual nature of wave and particle, hence wave-particle duality. that is pretty important, and if you dont know it by this stage id be a little worried.

I feel inclined to say this. Electrons are cathode rays, light is a photon. omnomnomnomnomnomonomonomoonomonoonomonomoonnmononom

 

[Beaconite]

Use your textbook m8

 

[someth1ng]

qualities of wave:
- diffract
- reflect
- refract

qualities of particle
- thomsons charge to mass ratio experiment showed light was of charged particle nature as mag + elec field deflected/attracted the light
- the paddle wheel experiment
- photoelectric effect

light has dual nature of wave and particle, hence wave-particle duality. that is pretty important, and if you dont know it by this stage id be a little worried.

Other properties for a wave include polarisation and interference.

In the context of light, it is NOT a changed particle. It is a photon, a particle with zero rest mass and no charge. If it were charged, you'd be electrocuted instantaneously and the paddle wheel was used for cathode rays NOT light - if it were for light, you'd be pushed in all direction due to the light's momentum.

 

[john-doe]

If it were charged, you'd be electrocuted instantaneously and the paddle wheel was used for cathode rays NOT light - if it were for light, you'd be pushed in all direction due to the light's momentum.

lol imagine that happening hahhahahaha

 

[someth1ng]

lol imagine that happening hahhahahaha

Wasn't joking...LOL