Physics

It is known that refraction occurs when wave pass from, say, deep water region to shollow water region, and wavelength of the wave decreases and hence the speed of the wave. I would like to know why this would occur in detail. I can't find any expanation in text book, and I was just told that it would occur. And beside, we all know that nuclei of atoms are composed of protons and neutrons, I just know that the reason of why neutrons and protons would be packed together is related to somewhat about nuclear force though I don't know the detail = =...

heya every1~! I had a quiz on electric fields and circuits a few days ago, and I got it back today. I was surprised to see 9/10 score as my expectations were very low. I think my teacher mistakenly gave me points on a question... The question is: Two resistors are wired in series with 24 V battery. R1 = 9 ohms and R2 = 18 ohms. Find the current through R1, and the power of R2. I got 8/3 A for current, and 32 W for power....are these accurate answers?

Anyone made past first round this year? If so, what did you to do prepare for this?

This is a high-school level question, I think. But I'm in high school We are told that a polaroid filter will only allow light to pass if it is polarized on the same axis as the filter. Otherwise, it will not get through. It follows, then, that if you pass light through two polaroid filters, you will get nothing through the other side. Empirically, we can test this, and it confirms what we know. So far so good. Now, say we take a third filter and put it in between the two previous ones. We turn it to a 45-degree angle from both of them. Now, if no light could get through the two filters before, then surely adding a filter would not change this. After all, a f…

If I have a specified number of light sources with known luminous flux and opening angle pointing in the same direction and with known distance from eachother, how can I calculate the total luminous flux? In a specific problem I have a 100 LEDs with 22 candela and a 20° opening angle which I calculated to give me 3300 lumen per lamp. However now I am unsure how much light the combined hundred lamps (aranged in a grid with 1cm distance) will give - as I strongly assume it wont be just 330.000 .

Hello. I have an obscure question... I understand that electromagnetic energy spectrum includes everything from Gamma Rays to Radio waves, with x-rays, light and microwaves somewhere in between. I also understand that fire releases energy. Much of this energy is heat, and some of it is light. In addition to light, what other forms of electromagnetic energy does a fire release? Does a fire also emit ultra-violet radiation or infrared radiation? What about X rays and Microwaves? Or even radio wave interference? And what would the distribution of this energy look like on a graph? I have attached an image of what I think it might look like, but I am pro…

And from what I understand about them (which is not very much) is that these two theories can not coexist. Again I know next to nothing about both of these but chaos theory says that you could theoretically predict any event if you know the initial conditions. Quantum physics on the other hand (and correct me if im wrong) says that you can only predict the probability of an event happening. I may be wrong on both of these but which is more accepted in the scientific community? Right now it seems like chaos theory makes a lot more sense but that may just be because i dont really understand quantum physics very much.

We just began looking at uniform electric fields at school and for the weekend we were given some problems to complete. I came to one of the problems which involved a concept i am unsure about and so have had trouble completing the problem. I am a unsure of what it means when something has been earthed, so would somebody be able to help me with the following problem, and also if possible, expalin to me what it means when somethng has been earthed: What would the potential difference be between two parallel plates if the upper plate is at a potential of 1000V and the lower plate is earthed?

Is there a minimal "portion" of time? Or the time can be "divided" on infinite number of parts?

They say that there is absolutely no zero referance frame for location or velocity, which is true. I think that there IS a zero frame for acceleration (this would be the acceleration where no external force is required), and that this is defined by the gravitational field where you are located. Where I am sat it is 9.8 m/s2 straight down. So in a sense the presence of mass, which causes gravity, defines the zero frame. However what about rotation? I would define this as the rotational angular velocity where no force is required to hold youself together - ie zero centrifugal force (although I know this is a misnomer). So what defines what this is? It does seem by coin…

What's the difference between the formula of [math]g = \frac{F_g}{m}[/math] and [math]abs(g) = G\frac{m}{r^2}[/math]? Note: abs(g) means absolute value. I don't know the latex code to input absolute. Because the question asked me: Calculate the gravitational field intensity 340 km above the planet Venus. I used the second formula above, where r = 340,000 m; G = 6.67 x 10^-11; m = 4.83 x 10^24 kg. I got [math]2786.859862 \frac{N}{kg}[/math] for the answer. Is this correct? I still don't know why I used the second formula, not the first one, though?

In a "Rotor-ride" at a carnival, riders are pressed against the inside wall of a vertical cylinder 2.0 m in radius rotating 1.1 revolutions per sec when the floor drops out. What minimum coefficent of friction is needed so a person would not slip out? Collecting the information from the question: [math]f = 1.1[/math] [math]r = 2.0 m[/math] [math]\mu = ?[/math] First, I used this formula: [math]a_c = 4\pi^2rf^2[/math] and it yielded [math] 95.5377706 m/s^2[/math]. To find the velocity you use: [math]v = \frac{2\pi2}{T}[/math]. Therefore, you need the value of [math]T[/math]. [math]T=\frac{1}{f}[/math], yielded [math]13.82300768 m/s[/math]. Next step, I k…

Hmm Ive been wrestling with this for a while now (hence my return to sfn ). It goes as follows; Imagine a wire of 0 resistance. OK so unless there's a rule of physics im missing then we arn't loosing any energy in the wire. So i decided to wave a flornscent tube around the wire. The magnetic fields around it make it glow. . So wheres the energy coming from? By introducing the florescent tube am i introducing a voltage drop?

http://en.wikipedia.org/wiki/Piezoelectricity I'd like to collect any further facts about "piezo-stuff".

I am new and I haven't really joined in much physics discussion because well, I just recently got interested in it. I've read a few books with general introductions to I guess "Modern physics" but there are a few things I don't understand. If you could help me out that would be great. Special Relativity /w General. 1) In regards to curvature of space and time, it seem to me that would imply a definite finite universe. Is that correct? Also is the curvature indefinite, like plastic deformation? 2) This Time dilation and length contraction, Here is the given example: "Consider two observers, each in a space-ship laboratory containing clocks and meter sticks.…

Hello, I am sure you have all already heard about the efforts in making wireless power happen. One way I am looking at this is I think electro magnetic power. You know you get those toothbrushes that you put on the stand and they charge without any cables. Well I am wondering how they do this! Also I would like to know if you could do it on a larger scale with a larger voltage and current!? Any help would be appreciated greatly! Thanks a lot

Hi all! It seems there are a lot of threads about black holes latley so how about we have a collection of useful information in one place as an easy reference source that can be used hen ansering these threads? First I'll start posting some links Wikipedia - Black Holes Black hole FAQ A guide to black holes Formation & Life of a black hole CGI of black holes Black holes and gravitational waves Linking black holes and string theory Lots of black hole information If anyone wants to post formulas, FAQ's, references, links etc. that would be great Cheers, Ryan Jones

Hi, I recently borrowed a book from local library for physics. It's called College Physics 2nd Edition by Raymond A Serway, Jerry S Faughn. I want to start studying this independently but I have no clue on how to approach it (i.e. where to start..). My official physics class is next year but I want to start early so I can get really good grades on the class. What would be good order of concepts that I need to learn? P.S. I didn't have physics before and I'm only a high school student. But I take calculus now and manage to score 100% in it so I guess I'm pretty decent at math. Thank you very much for your help!

Hey all, just taking more tangents from my revision again and thought about the following: ok so the world makes one full rotation in 24 hours, which means it spins 15 degrees in 1 hour etc etc. so if i was to jump vertically in the air and hover above the ground for 1 hour and then falls back down the same line an hour later would i be displaced 15 degrees horizontally? whichi guess physically is about the size of france. i was only wondering this because im off to america in the summer and the flight there and back take basically the same time. anyway cheers for any input! rob

I've seen lots of these used to kill mosquitoes in the night. Since they are attracted to the light, they approach the light and are zapped. Any idea how these devices work? I'm trying to build one.

I'm repairing a stereo and it seems an integrated circuit is damaged. I'm trying to replace it, but can't find the circuit in stores. It says (BA6191 345 111). I'm wondering if there's an alternate IC that can be used which can fulfill the same purpose. Perhaps there's another IC with the same specs but another part number?

We all know that gravity is a force associated with mass, but what in mass that causes gravity? Is it possible to get negative mass?

Definition Of A Metre The metre wa a unit of length was first determined in 1973 when the french government decreed it to be 1times10^-7 times the length of the warts quadrant passing through paris. The arc was surveyed and then three platinum standards and several iron copies were made. When it was discovered that the quadrant survey was incorrect, the metre was redefined as the diatance between two marks on a bar. In 1875 the systeme Internationale (SI) of units was set up so that the definition became more formal: a metre was the distance between the two lines scribed on a single bar of platinum-iridium alloy. Copies or 'artefacts'. were made for dissemination of t…

What jobs are available in physics? I know about a few e.g research, design, education even medical physics but can anyone think of any more?

Hi there, nice forums, and nice to potentially meet you (if 'meet' is the right word online). I have a question that I cannot answer, and cannot find any information on: What is the relation between frequency (pitch) of a soundwave and the distance it will travel before becoming inaudible? Any help appreciated, thankyou.