Physics

Hello. Blue plus red emitters are used as grow light. The resulting hue is the sum of red+blue. Or is it the difference ? If the sum; what color is the difference of their wavelengths ? And what is the intended meaning for 'full spectrum' ? (Image borrowed from the web)

I have found droplets (of water, I assume) inside my chocolate wrappers. The wrappers hadn't been opened and didn't have holes in them, but they had been stored temporarily in a humid environment by mistake for maybe 30 minutes (they were at room temperature prior). Are the droplets likely to be condensation?

Hello all. Never had it fully clear, voids in knowledge... If a solution has -say all- the elements dissolved in water, and a direct electric current is passed in it; what elements will deposit on the electrodes if the voltage is 0.1V ; if it is 0.2V; if it is 0.5V; ... ... ... if it is 1.0V ? Can you cite examples for each voltage please, and which table tells it ? Electronegativity ? Electrochemical series ? Standard electrode potentials ?

My kitchen lacks one of those gradually-adjustable lights. Sometimes when I get up in the middle of the night I want a light that's just bright enough to help me see what I'm doing when I eat, but not as bright as the overhead lights. Sometimes, therefore, I use the refrigerator's partly-opened door. I'm fully aware that the refrigerator doesn't just produce light, but also heat, from the fact that relocating heat from the interior of the refrigerator to the exterior thereof converts electrical energy to heat energy in the process. However... since this is the same thing my electrical heaters in my apartment do anyway... does that mean that, so long as I adjus…

Am I to assume the tradeoffs depend on the scale on which they're being used? For photovoltaics, I'm not sure industrial use would necessarily be any more efficient than household use, on a per-panel level, but for thermal!solar, it sounds almost like the reasons for higher efficiency follow from thermodynamics itself... larger array of mirrors mean more sun rays converged means more sun rays on the same area means higher maximum temperature meaning higher difference between warm and cold reservoirs of the heat engine, which from what I recall from thermodynamics is more efficient, all else held constant. How do the initial costs and maintenance costs of each …

According to Einstein, if you go faster than the speed of light, you go back in time. Obviously you can't go back in time in the literal sense of the word, but you can go back in time in the sense that you can enter a parallel dimension where t=-1 compared to the present universe where t=0. Is that true?

So recent events got me thinking about the politics that led us here, including the 2016 election and Martin O'Malley's so-called "rain tax". It taxed impermeable surfaces that cause water to pick up pollutants as it flows, and further damaged his already not-so-hopeful career. While Vox is defending this tax (or at least criticizing flawed criticisms of it); and I get realize that there is often more to these issues than some buzzword will let on; what I am wondering is why there wasn't infrastructure in place; whether on a local or federal level; to actually collect rainwater so it could be transported to where it could be used. Seems a waste to just let some mere lawn …

Does relativistic mass possess gravitational (passive) mass? Do you know any link that describes an experiment at CERN which proves or disproves the increase of weight in particle at near C?

Good day. Clearing the snow off my panels on he roof as it will be sunny the next week but still under 0oC and I wanted them generating, got curious... Sun does warm up solar panels, no doubt. Ambient too. But is panels heating only product of the solar radiation + environment or the panels themselves add warmth by the current produced ? In other words; a solar panel that has reached its temperature plateau under the sun while disconnected (no current flowing); it will increase its temperature when connected to a load and current flows, right ?

Sorry, if I am a bit off topic, but just a side question out of curiosity - can bouncing light in a fixed box have any wavelength, or only some discrete values?

A: In anticipation of future power outages, (last windstorm didn't do it but the next one could) I've been stuffing the top part of my freezer with tupperwaves full of ice. I'm figuring that because hot air rises and cold air sinks, that absorption of heat by melting ice would both preserve my frozen food for longer and double as an indication of how safe the food is by how much of the ice has melted. Would everything below this ice-water mixture be kept at 0 degrees centigrade due to sinking cold air, or is there something I'm missing? B: A little trickier is the question of how to keep items in refrigerator part well enough below room temperature for food no…

What got stuck in its development, what is the bottleneck ? Have heard nothing in almost a decade 😟

Just prepared: https://arxiv.org/pdf/2112.12557 While textbook explanation of p-n junction ( https://en.wikipedia.org/wiki/P–n_junction ) looks quite heuristic, this is just using statistical mechanics - no "holes", only electron dynamics. Lattice 60x30 atoms below, dopants of different potentials are presented as red/green dots, grayness shows calculated electron densities, arrows show local currents. The model is: - use 3 types of potentials: of individual atoms + from external voltage + mean-field self interaction (from found charge density), - apply entropy maximizing diffusion ( https://en.wikipedia.org/wiki/Maximal_entropy_random_walk ), getting e.…

Considering an atom within a rigid body, does the angular momentum of an electron within the atom vary when the body is put in motion?

So it's that time of year again; wintertime cyclones bring snow, then snow-melting rain, then the mixture of rainwater and meltwater can freeze in the colder temperatures that follow both. Typically I've only seen the latter on streets, not patios, though I'm not sure why if at all there isn't a risk of the same happening on patios, if for any reason marginally less so. I'm wondering what the most practical way to deal with that is. Is it better to shovel the snow off the patio before it transitions to rain, or does that just expose the rainwater to the subsequent cold temperatures? Conversely, if one were to deliberately leave the snow on the patio, to insula…

What does 'emergent' mean to you in a physics context, such as spacetime?

A light-hearted question... Every time I am in hurry filling up my water bottle before gym, I wonder the same thing: how much water should I pour into the bottle (then shake it vigorously and pour it out) for the best rinsing effect? Of course, I don't care much about the exact number - but I wonder how to even tackle the problem?

Okay, this is a simple question, but the context is a bit unconventional. There is a claim from a man named Bob Lazar that he was hired by the government in the 80's to help reverse engineer a UFO. He claims that the fuel used by the UFO(s) was a stable isotope of Element 115, AKA Moscovium. Obviously there is a lot of unpack there about the veracity of the claim and we could easily get off track. What I want to know is how you would know what it was you had in your hand. For the sake of argument, let's assume that a materials scientist had a stable isotope of element 115 about the size of a ping pong ball. I could be wrong, but I don't think spectroscopy woul…

This literally hurt my head when I read that statement in a book, the book was trying to prove that Physics rhymes historically to the point of the rhyme itself being the science instead of the Physics that we normally would pay attention to. In the first 3 pages of the book he writes in big bold letters dramatically, “ ‘THE YEAR OF 1-DERS’ SHOWS THAT ‘PHY-6’ BEGAN IN YEAR ‘1-666’ WHEN ‘NEW-TON’ CREATED HIS ‘NEW’ LAW OF ‘TON’! ” When I went to check if that was true it checked and I was scared. Have you ever heard anything like that before? And when younger more naive people here that statement this younger generation that is into entertainment and ra…

- Question "Gravity is the weakest of the four fundamental interactions of physics, approximately 1038 times weaker than the strong interaction, 1036 times weaker than the electromagnetic force and 1029 times weaker than the weak interaction. As a consequence, it has no significant influence at the level of subatomic particles.[4] In contrast, it is the dominant interaction at the macroscopic scale, and is the cause of the formation, shape and trajectory (orbit) of astronomical bodies." link: https://en.wikipedia.org/wiki/Gravity It seems to me that the gravity or gravitation adds or builds up in interaction from microscopic (e.g. sub-atomic particles) to macr…

If it were possible to ride a photon, what would our perception of time be like?

This question is for the physicists mainly, I suppose, though there may also be a philosophical element to it. (Mods may wish to relocate the thread as appropriate). I ask as an interested layman. We're routinely told--by scientists--that there are four fundamental forces of nature, one of which is gravity. This is so commonly heard that I assume quotations are unnecessary. Gravity construed as a force seems entirely unproblematic under the erstwhile Newtonian paradigm. But times have moved on . . . Much of the lay reading I've done in this area seems to suggest that general relativity--if read literally--treats gravity not as a force at all; rather, it is…

I've been, as of late, debating with rather fringe or crackpot physicists on ResearchGate and in the process of such an exchange i've found myself forced to be rather particular about my terminology. It was a debate regarding Special Relativity and the person in question made the obvious mistake of assuming that such a theory couldn't be extended to accelerating reference frames. I came to clarify to him that in Special Relativity you could only deal with reference frames that accelerate as a result of dynamical influences or forces as General Relativity would come into the case for accelerated motions without forces. In hindsight, it is relatively true this is the case i…

What I learned in physics about visible light is that the shorter the wavelength the more energy it has, thus red which has the longest wavelength is the outermost color on the rainbow because it bends the least, colors with longer wavelengths bend less and also have less energy. Likewise, violet has the shortest wavelength and that's why its the innermost color on the rainbow, because it bends the most with its short wavelength. Also since it has the shortest wavelength it has the most energy so therefore violet lasers are the most powerful. So this being the case I would like to say that Samuel Jackson is smart. Samuel Jackson who played Mace Windu wanted a purple…

There are plenty of explanations as to why light exists in different colors due to existing as different wavelengths, but what I can't find is any explanation as to why light exists as a variance of wavelengths in the first place. What process/force/function/whatever is it that gives rise to a spectrum of wavelengths as opposed to there just simply existing one wavelength?