Photons exert a gravitational attraction on massive particles. :psyduck:
[QUOTE=JohnnyMo1;32801972]Photons exert a gravitational attraction on massive particles. :psyduck:[/QUOTE]
the hell?
does that mean if you had a powerful enough laser you could shift an asteroid's trajectory without even hitting it with the photons?
I guess so.
It's because they contribute to the stress-energy tensor which is the actual source of gravitational field.
cool
[editline]16th October 2011[/editline]
wait... they contribute to the source of the gravitational field?
so photons on their own can warp spacetime?
[QUOTE=JohnnyMo1;32802145]I guess so.
It's because they contribute to the stress-energy tensor which is the actual source of gravitational field.[/QUOTE]
Wait, wait, I thought gravitons were the particles that transmitted grav. force. Do photons emit gravitons, Johnny? :psyduck:
Gravitons are hypothetical and also that's a different theoretical framework entirely which we've yet to reconcile with GR so to put it succinctly I don't fucking know man.
But is it accepted that photons exert grav. force, or does it have the same standing as gravitons?
Cause doesn't that put a huge damn dent in graviton theory? 'Cause I mean, if it's constantly emiting photons, it'd lose energy and, pretty blip out with sufficient time.
then again, I do recall reading that particles didn 't lose energy when they emitted heavy bosons so I dunno.
Even ignoring gravitons, under GR they'd be losing energy because they'd be emitting gravitational waves, I think. But yes, as far as I know this is generally accepted as a simple consequence of GR.
Anyone mind helping me with a few physics problems I have? It's for mastering physics (surprise sur-fucking-prise). I don't give a shit about getting the marks on mastering physics, I'm just trying to understand the content from the semester. I wish this stupid fucking site would give me some POINTERS and tell me what I'm doing wrong. There aren't even any hints this semester! Utter bullshit.
[quote]At what pressure ratio would a heat engine operating with a Brayton cycle have an efficiency of 80.0? Assume that the gas is diatomic.[/quote]
I tried going:
Efficiency = 1 - Qc/Qh, or 1 - Tc/Th with efficiency as 0.80, and then subbing in (pV/nR)c and (pV/nR)h for Tc/h but I'm not sure I'm approaching the problem right.
[quote]A Carnot refrigerator operating between -20.0 deg and 30.0 degrees Celsius extracts heat from the cold reservoir at the rate 100 J/s. What are (a) the coefficient of performance of this refrigerator, (b) the rate at which work is done on the refrigerator and (c) the rate at which heat is exhausted to the hot side?
What is the coefficient of performance of this refrigerator?
[B]5.06
Correct[/B]
What is the rate at which work is done on the refrigerator?
[B]Exhausted 3 of 4 attempts for this question.[/B]
What is the rate at which heat is exhausted to the hot side?
[B]Used 1 of 4 attempts.[/B]
[/quote]
This entire question is making me angry at myself. I've always been good at physics but just buggering this whole thing up is demoralizing me.
[quote]250 ml of water at 20.0 degrees Celsius is placed in the freezer compartment of a refrigerator with a coefficient of performance of 4.00. How much heat energy is exhausted into the room as the water is changed to ice at -20.0 degrees Celsius?[/quote]
Got 0% for that problem. Tried using Q = mcT with the change in temperature 40 degrees AND 20 degrees and then relating it to COP = Qc/Qh-Qc, but that got me nowhere. Help on working through it (even though I can't get any marks now) would be appreciated.
[quote]The power output of a car engine running at 3000 rpm is 500 kW.
How much work is done per cycle if the engine's thermal efficiency is 40.0?Give your answer in kJ.
[B]10.0 kJ
Correct[/B]
How much heat is exhausted per cycle if the engine's thermal efficiency is 40.0?Give your answer in kJ.
[b]Used all my attempts on this. Want to know what the answer is, and how to do it, though[/b][/quote]
I miss quantum mechanics and relativity :( That shit was easy. This stuff is pissing me off.
Another quick question guys
When bombarded with electrons, why does a copper anode give off X-rays of two discrete wavelengths? I'm raking my textbook for answers, but I can't seem to find anything
[editline]17th October 2011[/editline]
My answer is something nondescript to do with having two energy levels that electrons can be demoted from to release x-rays
[QUOTE=Turnips5;32830283]Another quick question guys
When bombarded with electrons, why does a copper anode give off X-rays of two discrete wavelengths? I'm raking my textbook for answers, but I can't seem to find anything
[editline]17th October 2011[/editline]
My answer is something nondescript to do with having two energy levels that electrons can be demoted from to release x-rays[/QUOTE]
the way that occurs to me as being the most probable is something vaguely analogous to phosphorescence - electron goes in and promotes an electron to an excited state. drops back down to ground state - energy emitted will be at a characteristic wavelength based on the energy gap between ground and excited state. in this case obviously there are two transitions that cause emission in the x-ray area of the spectrum.
this will vary from species to species, depends on nucleus, electron screening etc. this is just an educated guess but it's probably correct.
[QUOTE=mike;32833620]the way that occurs to me as being the most probable is something vaguely analogous to phosphorescence - electron goes in and promotes an electron to an excited state. drops back down to ground state - energy emitted will be at a characteristic wavelength based on the energy gap between ground and excited state. in this case obviously there are two transitions that cause emission in the x-ray area of the spectrum.
this will vary from species to species, depends on nucleus, electron screening etc. this is just an educated guess but it's probably correct.[/QUOTE]
Okay, cool. That's pretty much the gist of what I put down, thanks!
[editline]17th October 2011[/editline]
Yesss, finished all my weekly coursework and lab preparation a day early. Feels excellent man.
okay, that is hands down the coolest fucking thing ever
I've seen it before but never in such good quality
What is this magic?
Meissner effect
it happens when you cool a certain kind of material below a critical temperature and it becomes a superconductor, and then yeah fuck it it's magic
[url]http://en.wikipedia.org/wiki/Meissner_effect[/url]
I've seen it firsthand. :D
plz explain johnnymoo
[QUOTE=Jo The Shmo;32836703][media]http://www.youtube.com/watch?v=Ws6AAhTw7RA[/media][/QUOTE]
SCIENCE, BITCHES!
Also Jews.
That was a pretty good x-ray diffraction experiment.
Got three really good results all giving 2.01*10^-10m (201 picometres) for the atomic spacing, just looked it up and apparently that's almost exactly right. YES!
I love it when you get nigh-on perfect data, and spectrometers with diffraction gratings seem to always give excellent results. It's a refreshing change from being given crap equipment to do an experiment that seems questionably valid and getting shite data.
Undergraduate experimental physics >>> A-level experimental physics
I haven't done the data analysis for my x-ray diffraction experiment yet.
I need to do an errors analysis and conclusion, which I'll do tomorrow a while 'fore I have to hand it in.
Is your experiment the same deal as mine? For me it was just finding Bragg conditions with a lithium fluoride crystal. I bet you do more interesting things with x-ray diffraction in higher years.
I think the guys who do MasteringPhysics should do a MasteringAnger to stop me from destroying my computer after trying to do MasteringPhysics
It will just replace your anger with sadness.
[QUOTE=Collin665;32878850]It will just replace your anger with sadness.[/QUOTE]
MasteringSadness
[QUOTE=Turnips5;32879119]MasteringSadness[/QUOTE]
:smith:
[editline]21st October 2011[/editline]
Hey guys, I'm wondering if someone here can help me on a homework problem I am stuck on.
My work so far appears at the bottom.
[IMG]http://oi52.tinypic.com/34931hf.jpg[/IMG]
Am I supposed to realize that u-sub-b-bra*U-dagger equals v-sub-b-bra or something? If so, how do I show that?
So apparently my lab professor died the other night
Was he a good teacher?
Also, I'm divided between two courses, condensed matter or particle physics.
I'm tending towards particle physics but it has a heap of bio medical shit and instrumental shit.
I dunno, he barely taught us. The lab was largely run by the TA, who is I guess the de facto professor for now.
damn that sucks Johnny, sad to hear it
Sorry, you need to Log In to post a reply to this thread.
