Sign Definition and 596 Threads

My textbook does a very poor job of explaining how to assign signs to power: http://www.mediafire.com/view/?e0xr8j41tokujx6 It goes on to explain passive sign convention but it never explains active sign convention. Also, shouldn't the sign for power depend on voltage and current since power is...

I believe that I have found a serious mistake in the wiki entry about Potential Energy. notice the -ve sign in the formula on the web page. According to the article, the definition of this term is : the gravitational potential at a location is equal to the work (energy transferred) per...

If a Feynman diagram only involves bosons, then can you multiply all external 4-momenta by negative one, and still get the same amplitude? Looking at the Feynman rules this seems true. If the diagram has a fermion (as real or virtual particle), then it seems this is no longer true. I just...

Homework Statement Dear all I have a question concerning the Coriolis acceleration expression. I learned it as Ac = -2ω x v, where ω is the vector which indicates the rotation axis direction of Earth and v the velocity of a body that I want to check the Coriolis effect on. My...

Dear all I have a question concerning the Coriolis acceleration expression. I learned it as Ac = -2ω x v, where ω is the vector which indicates the rotation axis direction of Earth and v the velocity of a body that I want to check the Coriolis effect on. My question: where the minus...

Homework Statement When calculating the P-value, must you change the sign of the test statistic depending on the type of test (lower, upper)? For example, if your calculated test statistic is t=2.5 and you want to perform a lower-tailed test, is your answer the cumulative probability of...

Homework Statement Question is in attachment Can someone explain to me what the infinity sign is I'm new to this topic. All I know is that as a satellite goes to a higher orbit that the velocity decreases.

Prove the Identity by Using a Sign Reversing Involution (See Attachment)

In this question, my answer to part (a) is correct, & leads into (b). With (b) my answer is also correct, except for the sign. Can anyone help me figure what I need to do? Many thanks. Homework Statement Q. 90^{\circ}<A<180^{\circ} such that...

"Hog Crossing" sign needed on new Texas highway http://www.cnn.com/video/?hpt=hp_t3#/video/us/2012/10/26/dnt-wild-hog-packs.kxan Imagine hitting one of those porkers at 85 mph! :eek:

On the book Conformal Field Theory by Francesco, Mathieu and Senechal (the yellow book), in the derivation of the propagator kernel K(\delta t,\xi,\xi') on (2.73), the signs on the first and second line just doesn't match. On first line it has -\xi^+ T \xi'-{\xi'}^+ T \xi' while the second...

Homework Statement A ball is dropped and rebounds vertically to less than the original height. For this first bounce only, sketch the graph of (a) velocity against time (2) (b) acceleration against time (2) Homework Equations The solution I have for the acceleration time graph...

Homework Statement The problem asks us to write a MATLAB function that takes as input a vector 'v' representing a 64-bit machine number in double precision, and extract the sign (t), the exponent (c), and the mantissa (f). Homework Equations The Attempt at a Solution I'm extremely novice at...

Homework Statement solve ∫log(1+acosx) by differentiation under integral sign (limits are 0 to ∏) Homework Equations The Attempt at a Solution =∫(1/1+acosx)cosxdx(by leibinitz by differentiating partially WRT a. Then how do I proceed,can anyone show me all the steps of...

Sometimes I have seen a dash (-) being used as multiplication sign, usually in connection with units. Does anybody know where this strange custom has it's origin?

Homework Statement A sign hangs precariously from your prof's office door. Calculate the magnitude of the tension in string 1, if theta1 = 35.67°, theta2 = 62.43°, and the mass of the sign is 3.3 kg. Homework Equations The Attempt at a Solution Ft1=cos35.67t1 + cos117.57t2=0...

I thought passive sign convention is obeyed when you have a positive current flowing into the positive terminal of the element first. But how about this case? While it is drawn that way, the positive terminal is actually the NEGATIVE terminal because the voltage is negative, so you have to flip...

Homework Statement The work done by an external force to move a -8.50 mu C charge from point a to point b is 1.90×10^-3 J. If the charge was started from rest and had 4.86×10^-4 J of kinetic energy when it reached point b, what must be the potential difference between a and b...

Homework Statement What is sign convention, and how is it applied to vectors? I was reading an economics paper when I came across this term. There's a ":" sign between the vector in question and an entry, which is all supposed to output a real number. What exactly is sign convention, and how...

From the attached image, the net force on the 1.0mC charge is zero. What is the sign and magnitude of the unknown charge q? Here is what I did: F = k QQ / r2 F = 9.0x109Nm2/C2*(0.002C)*(0.001C) / (0.05m)2 F = 7.2 x 106N Then to look for the unknown charge: F = k QQ / r2 Q = F* r2 / k Q Q =...

Why do attractive force have a negative sign? The book says its because one must be moving toward the other. But how does it make it negative? I don't understand. Can anyone explain the law of gravitation formula?? F= -GMm/r^2

Here is a petition about supporting pi against tau. So if you think that pi should not be changed, please sign this petition: http://www.change.org/petitions/khan-academy-withdraw-the-support-for-tau. I'm not sure if the petition will help, but... P.S. If this petitions are not allowed, by...

Why is the unit vector for time in Minkowski space i.e. the fourth dimension unit vector always opposite in sign to the three other unit vectors? The standard signature for Minkowski spacetime is either (-,+,+,+) or (+,-,-,-). Is there some particular reason or advantage for making time...

Hello, I am trying to reproduce Bell's calculation for the expectation value of paired spin measurements on particles in the singlet state. For unit vectors \hat{a} and \hat{b} we want to calculate P(a,b)=<\psi|(\hat{a}\cdot\vec{\sigma})(\hat{b} \cdot \vec{\sigma})|\psi> where...

Consider a biresonant transformer with a small coupling coefficient k << 1. Let the voltage applied to the primary LC circuit be U1(t)=U*sin(2*Pi*f*t), then also the current I1 will be sinusoidal. The voltage induced in the secondary winding and the current in the secondary LC circuit will be a...

I have attached the image of the clipper circuit below. When Vin is positive the diode is reverse biased and the output and input are at the same loop. When Vin is negative the diode is forward biased and Vo=0. My problem is finding the sign of the output, although I know that Vo and Vin are...

I have attached an image of a clipper circuit below. First Question: When the sinusoidal input is positive or negative, how do i know how to label it in the

Hello, I'm trying to figure out what hypothesis I need to swap the Re{} (or Im) operator and the integral sign, but I can't find anything on the matter. I guess either it's a trivial question or a rare one. Can someone help me? Thanks in advance.

I don't know much about brackets and Hamiltonians, but there is a much simpler aspect of the time / energy uncertainty discussion that confuses me. It has to do with the sign of the uncertainty. [Disclaimer: Purists, please bear with me for a moment as I hash out my point heuristically.]...

Hello, I believe this is a really stupid question but I can't seem to figure it out. So given a Minkowski spacetime one can choose either the convention (-+++) or (+---). Supposedly it's the same. But given the example of the four momentum: Choosing (+---) in a momentarily comoving...

Homework Statement R(x) := ∫ exp ( -y^2 - x^2/y^2 ) dy The Attempt at a Solution I move the derivative operator inside the integral and differentiate with respect to x R'(x) = ∫ [ - 2x/y^2 ] exp ( -x^2/y^2 - y^2 ) dy Then I let: t = x/y and dy = - x/t^2 dt R'(x) = 2 ∫ [ - x ] [ t^2 /...

Greetings, How do we decide on which sign to take when using the momentum operator? The question may be very simple but I need a push in the right direction. Many thanks.

OK, I realize I am probably on a hiding to nothing here, but please bear with me for now, I have tested my calculations so carefully that I am totally convinced that I have found an error in two published accounts of the BL line element . . . The first is Visser, equation (57)...

the potential difference between b and a is defined as follows: V(b) - V(a) = -∫E \bulletdl the integral is taken from a to b. so the potential of a positive charge, with infinity as reference, is V(r) - V(infinity) = V(r) = -∫E \bulletdl the integral is from infinity to r...

Homework Statement Compute the surface integral for F = [3x^2, y^22, 0] and S being a portion of the plane r(u,v)=[u,v,2u+3v], 0≤u≤2, −1≤v≤1.The Attempt at a Solution I managed to get the correct answer, because with some luck I defined the normal in the correct direction. I am just confused...

Homework Statement I just did a question on a charge moving relative to a stationary charge from an initial position x1 to a final position x2. I was under the impression that for questions involving coulombs law, and the equations for Electric Field Strength, Force and Potential we ignore any...

Hi all, I went to an engineering school 40 years ago but never finished, so I kind of know that this is easily solveable. I have a triangular sign 12' long (attached to wall) that is 2 1/2' thick and sticks out from the wall 6'. If I use 2 guy wires anchored to the wall 12' apart, that...

Homework Statement A resistor made from a shell with an inner radius r1 and an outer radius r2 hasa conductivity sigma. The current flows radially outward. 1.What direction does the E field point in. 2. Is the potential difference V2-V1 positive or negative. Homework Equations None...

Frictional force-- sign convention For a horizontal spring mass system is the frictional force considered negative (-μmg)? i guess it will be negative; the minus sign used to convey the force is trying to impede the motion of block then with that guessing work; i think friction force will be...

(\frac{\partial z}{\partial x})y the small y, what does it mean. the context this is used in is F(x,y,z) where each variable is a function of the other 2 variables.

how can you tell if a binary number is negative or positive? 1111 <--- how do you know if this is 15 or -1? and for my project i have to make a 4 bit subtracter using LED lights to show 1's or 0's. Do I just leave it in 2's complement form?

Homework Statement What does the real number sign with a + under it mean? Check the example below. Homework Equations http://upload.wikimedia.org/wikibooks/en/math/8/d/3/8d380fa4b673b84ddb613bed8ab8f189.png The Attempt at a Solution Tried Googling, but didn't find anything.

Homework Statement I know that the work done by an electrostatic force is given by : W = Fdcosθ (scalar product) W = qE d cosθ and I know that the electric potential is V = -W/q , where the work here is the work done by the electrostatic force. 2. The attempt at a solution...

Homework Statement A sign is on a truck traveling 55mp/h (88 km/h). There is a crosswind on the truck of 40 mp/h (64.37 km/h). What is the torque experienced by the sign from the crosswind? The sign is actually 2 boxes sitting side by side with identical dimensions. Following dimensions are...

I'm confused regarding why the double modulus sign is used. Let's take the dot product: u.v=|u||v|cosθ The R>H>S means that the cosine of the angle is multiplied witht the magnitudes of both vectors. Now, u.v=||u||||v||cosθ Does this mean the same thing? Help?

Hi! I'm having some trouble with optics. When we have convex, planoconvex, concave, planoconcave, and meniscus lenses, I don't understand how to substitute with the sign for R1 and R2. How do I determine whether the radius of a side is negative or positive? A book that I'm using said to take...

Homework Statement Prove that any function f(x) can be approximated to any accuracy by a linear combination of sign functions as: f(x) ≈f(x_{0})+ \sum{[f(x_{i+1})-f(x_{i})]} \frac{1+ sgn(x -x_i)}{2} Homework Equations The Attempt at a Solution Looks like taylors theorem...

I read through all of the previous sign convention posts on this forum (and googled a lot and checked a bunch of textbooks) before posting this question. I don't understand the sign convention properly for geometric optics. There are two conventions that I've understood so far, and I've got a...

[b]1.Hey guys, I've been struggling with this one for an hour and it SHOULD NOT be this hard for me. A 15kg picture hangs from a hook on the wall. What is the tension in each wire if one is at a cartesian angle of 220° and one is at a cartesian angle of 320°? [b]2. So my physics...

If a mass was hanging vertically from a spring under its own weight. In the static equilibrium position, using up as positive, the spring force is +kx and gravity is -mg. Add them up to get: kx - mg = 0. Using down as positive, the spring force is -kx and gravity is +mg. Add them: -kx + mg =...