Focus Definition and 200 Threads

I'm trying to find the polar equation first, and I learned this today but I forgot a lot of it and we're not allowed to take notes in class (professor says it helps to learn better) so I'm trying to look it up online but it's not much help because I can't find any elementary lessons on polar...

So I found the equation for the perpendicular line to the directrix in order to find the vertex, which I got the line y = x that is perpendicular to the directrix, then solved the system of equations to find the common intersection point, which was (1,1). I used the midpoint formula from the...

Hello All! First of all excuse my query which may seem trivial to some of you, I am about to purchase a laptop for work. I am an ECU programmer (engine control unit) / embedded engineer working for an automotive tuning company and I'm looking to buy a laptop suited for my programming needs. I...

autofocus...which subject does it focus on? Hello Forum, I was just reading and learning about autofocus. There are two types: active and passive, etc... But I am still missing on which subject on the scene does the camera decide to focus on? Focusing means changing the distance between...

I admit I don't know anything about string theory (nobody really does at an undergraduate level) but it sounds interesting and seems like something challenging. I am majoring in physics and maths but I am getting to the point in my undergraduate studies where I can begin to specialize more in my...

I'm a second year undergrad, currently majoring both in mathematics and physics. However I've decided that the time has come where I should stop taking both classes evenly and start devoting more of my time to one field. However I'm unsure which field that should be if I'm interested primarily...

I just had this question in an online test I took, and first I had 16ft, but for some unknown reason I chose to change it to 64ft right before I submitted the test, and of course I got it wrong. So I just want to confirm the answer is indeed 16ft.Homework Statement A parabolic antenna has a...

For those who don't know, a company (Lytro) just released a camera that allows for changes in focus *after* the image was acquired. Now that's it's been released as an actual product, I'm intensely curious to understand how it works. Their website has a cutaway image, and the 'lightfield...

I know that lasers will always have divergence due to diffraction. With that said, they don't diverge until after the point of focus, correct? Is there a limit to how far a laser can be focused?

Hi, As part of my portfolio for my end of semester math classes, I am trying to develop the equation for a parabola at an arbitrary rotation. I have seen it done based off of substituting X and Y variables with trig terms, and I am confident I could prove it that way, but I am curious if I...

http://www.bbc.co.uk/news/world-asia-15715446 I wanted to create a thread for monitoring U.S. and Asia-Pacific related developments and related analysis articles on those developments. I think Asia-Pacific developments will keep on catching media attention for coming many decades after we...

Homework Statement A person can focus objects clearly only between 15 cm and 40 cm. What eyeglasses would you prescribeHomework Equations 1/p+1/q=1/f P=1/fThe Attempt at a Solution I don't really know what to use for p, or f

Wish to focus on LED lighting technology, Mainly high powered LEDs to illuminate areas such as indoor and outdoor areas. Which masters area should I take into consideration? Should I consider getting a P.E.? Main things to consider when designing actual light fixtures; Optics Heat...

I posted earlier asking if my science fair idea—to use many mirrors to reflect light onto one point—would work. After getting a reply that it would, I now have another question. It's clear that I have to use a curved board to mount the mirrors onto, or I would just get reflection of straight...

Please don't leave out very many steps, please do give the formulas if possible please thank you: How did they get these values? Focus = (0,7/16) directrix = -7/16 Tried to use p=1/4(a) which DID NOT work , that yields p = 1 THEN the focus would be (0,1) which it is not. Teacher said to use...

Concerning the Convex Lens and my diagram attached, when an object is placed exactly at the principle focus (focal point) of the convex lens, if we apply the concept of Light Ray Diagram, the Principle Ray and Centre Ray after refraction does not intersect. From here, with 2 refracted ray...

Hi everybody, nice to meet you all I'm studing Physics in Catania University, Italy, and I'll get the master degree in Physics next summer. My thesis will be on plasma focus and I will spend a period in Bologna, DIENCA laboratories to work on it. I would like to know if there will be any...

Hey Everyone just wanted to know what topics are assumed knowledge in a math degree.

Homework Statement A glass lens (n=1.50) in air has a power of +5.2 diopters. What would its power be if it were submerged in water?Homework Equations Not too sure. May be Lensmaker's Equation, Snell's Law, and Power of a Lens Equation.The Attempt at a Solution I'm trying to derive the...

How big should a lens be to focus enough light to reach 1000 Celcius? I was wondering how big should a glass lens be to focus enough light to produce a temperature of about 1000 celcius at its foci? What if the lens was made up of sth with higher refractive index, doesn't this reduce the...

Hello all, I'm trying to decide whether or not I'd be interested in pursuing a specialized Electrical Engineering degree in one of the many offered "Focus Areas" at my university, but I'm not sure which one best suits me. I have a tough time deiciding which focus area to pursure because as...

Hello everyone, this is an amazing forum! :) I have a question: I have seen the formulas for focus/directrix of a parabola, but I cannot trust something unless I know how to get there. How do I get the formulas of focus and directrix? I got to an equation (X - Xf)^2 + (Y - Yf)^2 = (Y -...

Homework Statement Find the equation of a parabola with a vertex of (1,-3) and focus of (1,-1)? Homework Equations The Attempt at a Solution

OK - Here's a challenge. Our school has a theodolite; its telescope worked in the past. Now it suddenly won't focus beyond 7', though it gives a great image of objects between roughly 3'-7' away. The focus knob seems to move freely. My thought is that the eyepiece optics somehow got...

Hi all! I’ve always been in love with mathematics and physics. I’m 39 and have a full time job and a great deal of time to study after work, but I don’t have the possibility of attending to a physics college and go for a degree, because of timetables of available universities (or I would go...

I'm going to attend university and study mathematics in about 1 and a half years. As I want to devote myself and study the field for lifelong, I'd been thinking it wouldn't be a bad idea to start doing private study already. I'd like to ask for suggestions about what exactly would be the best to...

Hi everyone, Im currently in the way of learning about fusion to prepare myself for a thesis in this area. The method of colliding beams was what came to my mind the most naturally at first and it has catched my interest ever since. So, this is what i want to ask: Is there any serious...

Hi, I'm trying to write a C program to build an ellipse given 3 points and the focus equals to (0,0); can someone help me out? Regards, CPtolemy

You know how orbits are made of ellipses and ellipses are made out of two foci? I'm trying to find a formula where I can extract the position of the other focus point, relative to (0,0). By the other focus point I mean the one that's generally out in space. Very much like how the...

Hi, I have what might seem like an odd question. Suppose that someone is looking at an object in the distance, and there is an object placed about an inch in front of one of the person's eye. Obviously, this object would appear out of focus. My question is this: how would one bring this...

Homework Statement Ellipse with vertex at (2,3) and (-4,3) and focus at (1,3) Homework Equations (x-h)2/a2 + (y-k)2/b2=1 The Attempt at a Solution (h,k)= (-1,3) a2=9 (x+1)2/ b2 + (y-3)2/ 92

Visual information arrives via photons of visible light. These, we are assured, all travel at the same speed and therefore have the same impact. Why then, do those that travel a little further require a change in the shape of the receiving lens? In particular, nearby objects at distances of...

Hi, I am in need of some expert advice please. I am enrolling for my honours degree in mathematics next year. I am trying to mix it up in order to have a strong foundation in pure mathematics with specialisation in applied mathematics. My interests are financial mathematics, probability...

I unofficially have a PhD place at a great university to study an area of research in Physics that is not *quite* in the area that really interests me. How easily do people "move around" with their research after their PhD? I am interested in Dark Matter, and my PhD would be working on Gamma...

Even though, it is two years off, I need to start thinking about what I want to do with BS in Physics/math minor. Time will fly, I'm sure. Right off the bat, I'd like to get into graduate school if my grades are good enough. Frankly, I go to an upper-level Tier 2 school. Ideally, I'd like to get...

Homework Statement Find the equation of the parabola with focus (0, -4) and directrix y = -2 i barely understand this thing. i mean how do i find the vertex. the book says D1 = focus to any point on the graph, and D2= the point on the graph to the directrix. and D1 = D2. how do i graph if...

I am currently a junior year mechanical engineering major. I have always been interested in programming and throughout the years read books on C and Java. I recently started focusing on MATLAB. We've always had to use it in some of our classes, but I never really dedicated myself to learning...

Homework Statement Three forces act simultaneously on a 2.70-kg block. For clarity the drawings show the forces separately. The block starts from rest and, as a result of the combined action of the forces, undergoes a displacement s, which has a magnitude of 6.50 m. What is the final speed...

I have just finished my first semester of college so I have yet to begin working on my EE degree. However I'd like to think of the future as a source of motivation (my main problem) At my school studying EE has two tracks, computer or systems design. Same degree but slightly different...

So, I've been wondering. Anyone know what shape/prescription a contact lens would have to be in order for an eye to be able to focus on something 1mm away (assuming the distance of focus in the eye is around 4 cm)? Does it have to do with focal length of the lens?

Should I focus more on my physics and math "classes"? To get things straight, I'm not talking about learning the subjects (physics and math) I mean going through the motions such as calculating how much time to study for each subject so as to get x and y grades. Do physics graduate schools...

Hi, This is my first post but I've perused the forums often enough before (usually while I should be studying instead!). I'm 26 and in my second year of a 4 year Electrical Engineering degree (late starter). I am currently intrigued by radar and how to engineer machines to detect and track an...

Homework Statement This problem is from the Australian HSC mathematics extension 2 exam. Q6ciii) It states: Find the focus, S, of the parabola y^2=r^2+c^2-2cx where r and c are constants. The Attempt at a Solution I couldn't figure out how to convert this into the parabola focus...

We're currently using Stewart's in my class, and I'm not at all happy with it. I actually liked Stewart's for single variable, but the multivariable volume feels like it rushes over all the concepts and provides very little insight, and the problems are WAY too easy. They are useless for...

Homework Statement Prove that a vertical line and a line going from a point on a parabola to the focus of the parabola form equal angles with the tangent line of the point on the parabola. Homework Equations Focus = 1/4a (maybe relevant) The Attempt at a Solution I know how to...

Well I want to become an AE but want to know what it entails first. I want to focus mainly on Jet engines and propulsion systems mostly but if I have no real idea what that means or what it involves so can someone explain this to me? I think it means me and a group go out design,build and...

Homework Statement Use completing the square method to rewrite the equation of the parabola y^2 – 4y – 44 = 16x in the form (y-y0)^2 = 4A(x-x0) Hence find: a) the coordinates of the vertex b) the coordinates of the focus c) the equation of the line that passes through the focus...

I invite you to take a new look at http://focusfusion.org/" After a long search for funding, Eric Lerner and his team from LPP are really on the move now, constructing a new, most powerful DPF (Dense Plasma Focus) machine, exclusively devoted to fusion research, that should deliver a...

Homework Statement I am a bit rusty on parabolae. I am doing a question on projectiles and have found the coordinates of the vertex of a parabola as: (\frac{(v_0)^2\sin\alpha\cos\alpha}{g},\frac{(v_0)^2(\sin^2\alpha)}{2g}) The question now requires you to show that the distance...

Hey everyone, I'm entering my second undergraduate year as an astronomy and physics double major. I've always had an interest in black holes, high energy astrophysics, and cosmology; consequentially, I've planned to study one of these in graduate school. However, over the summer I've been...