What is Sign convention: Definition and 69 Discussions

In physics, a sign convention is a choice of the physical significance of signs (plus or minus) for a set of quantities, in a case where the choice of sign is arbitrary. "Arbitrary" here means that the same physical system can be correctly described using different choices for the signs, as long as one set of definitions is used consistently. The choices made may differ between authors. Disagreement about sign conventions is a frequent source of confusion, frustration, misunderstandings, and even outright errors in scientific work. In general, a sign convention is a special case of a choice of coordinate system for the case of one dimension.
Sometimes, the term "sign convention" is used more broadly to include factors of i and 2π, rather than just choices of sign.

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  1. L

    Electric potential - doubt in sign convention

    Electric potential --- doubt in sign convention Homework Statement Revered members, I know dV = -E.dx so E = -dV/dx So E should be E = -V/x . But while deriving capacitance of a parallel plate capacitor when dielectric medium is introduced we use E = V/x. But how E = V/x? Homework...
  2. C

    Understanding the Passive Sign Convention: Explaining P=+iv and P=-iv

    From what I understand: P=+iv (current enters through the positive polarity of the voltage, implying that the element is absorbing power) and P=-iv (current enters through the negative polarity of the voltage, implying that the element is releasing or supplying power) I remember reading that...
  3. P

    Sign convention of bolometric correction

    Okay I realize that stars emit at least some radiation outside the visual range but I have seen stars with positive BC when I thought that most values are negative due to the radiant flux over all wavelengths being greater than its flux over a certain wavelength. Is the sign of the BC the same...
  4. M

    Power Sign Convention: Confused? Get Help Here!

    Hey guys, So the sign convention for power is really confusing me. According to my knowledge, if a positive current is entering the positive terminal of an element, the voltage drops across the element and power is hence absorbed. Why does the question solution change the sign of the current...
  5. I

    Metric Sign Convention: Effects on Klein Gordon & Dirac Equations

    The two standard conventions for the Minkowski metric are diag(1,-1,-1,-1) and diag(-1,1,1,1). The physics comes out the same either way, but I'm trying to make a list of the things that change depending on the convention you use. The Klein Gordon equation is one - with the "mostly plus"...
  6. C

    Do All Circuit Elements Follow the Passive Sign Convention?

    Homework Statement 1) Q. Which of the elements follow the passive sign convention? (psc) http://img401.imageshack.us/img401/3092/pic1r.gif v1 = +5 (V) i1 = +2 (mA) v2 = -10 (V) i2 = +500 (µA) v3 = +1 (V) i3 = -3 (mA) 2) Q. Which of the elements follow the passive sign...
  7. E

    What is the Sign Convention for Work Done on a Gas in an Isothermal Expansion?

    Homework Statement One mole of an ideal gas at 300K expands isothermally from a pressure of 2x10^6 Nm^-2 to a pressure of 2x10^5 Nm^-2. Calculate the work done ON the gas. Homework Equations dW = PdV The Attempt at a Solution Following through the integral, it becomes clear that work is...
  8. C

    Power in voltage/current sources, passive sign convention

    Homework Statement Determine which of the five sources in Fig. (attached) are being charged (absorbing positive power), and show that the algebraic sum of the five absorbed power values is zero. I've labelled how I'm referring to the sources in red...
  9. E

    Convex mirrors - Sign convention trouble

    Homework Statement I solved the problem, but upon further observation, I discovered that what I did didn't make sense. (these are rounded numbers, which shouldn't make a difference in my question) do = 13 cm (do is what I solved for in the problem, and according to the online system it was...
  10. A

    Engineering Passive Sign Convention in circuit

    Homework Statement Calculate the power in the voltage source for this given circuit: Homework Equations P = \frac{V^2}{R} Or P = - \frac{V^2}{R} The Attempt at a Solution If we take the bottom left corner as the Initial node then and go around the circuit, then the voltage is a...
  11. C

    Why we call 'Passive' sign convention?

    Hello, It's my first time login. I'm not good at english. Of course, I'm not native speaker. I wonder why we call 'passve' sign convention. have a good day. :)
  12. redtree

    Sign convention in the space-time 4-vector

    What is the rationale for the sign convention in the space-time 4-vector? How is it related to the sign convention in the energy-momentum 4-vector, if at all?
  13. R

    Sign Convention - Physics - Optics

    [SOLVED] Sign Convention - Physics - Optics I was just looking at some sign conventions and I was wondering if this is true: Along the principle axis, if Si > 0, then does that mean you have a real, inverted image? Also along the principle axis, if So < 0, then does that mean you have a...
  14. R

    Voltage - Sign convention problems

    Hey guys, I need some help clearing up voltage signs, its always confusing me and I have my final this Friday. First off I'm not talking about voltage in a circuit, but rather if there is an electric field caused by a charge distribution. First off, I understand potential energy for gravity...
  15. Alpha Russ Omega

    Does this device follow Passive Sign Convention?

    Hello: I need help determining if I and V assignments follow the passive sign convention. Here is the image of the circuit: http://img178.imageshack.us/img178/9572/pic1xu2.gif I know that in order for it to follow PSC the current I needs to flow towards +V. I'm not sure if that is...
  16. F

    Passive sign convention (negative watts, and negative current confusion)

    This is my (error full?) understanding from my readings: 1. positive current flowing into a positive terminal of let's say a rechargeable battery is power being absorbed by the battery...so positive watts 2. negative current flowing into a positive terminal encounters the higher electrical...
  17. A

    Quick question on sign convention for Work in Columbs

    Homework Statement http://online.physics.uiuc.edu/cgi/courses/shell/phys102/fall06/prep2a.pl?practice/exam1/fa06 Homework Equations W =F*D The Attempt at a Solution I have it solved, now i thought - would be if i put work into the thing to move it but looking at it since both of...
  18. E

    Is the Work Done on a System Positive When There is Compression?

    In terms of the thermodynamic identity: dU = {\tau}d{\sigma} - pdV the term for the work done on the system (-pdV) must be positive if there is a compression, in which case dV would be negative, correct? If one wanted to write the identity in terms of the work done *by* the system, you...
  19. maverick280857

    Sign Convention for Geometrical Optics

    Hi Could someone point me to websites with tutorials on the real-virtual sign convention for geometric optics (and possibly other known conventions too)? I've been googling for some time but the results aren't too satisfying. PS--Tutorials with mathematics are preferred... Thanks and...
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