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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 consiste
Illustration of the "reference directions" of the current (), voltage (), and power () variables used in the passive sign convention.If positive current is defined as flowing into the device terminal which is defined to be positive voltage, then positive power (big arrow) given by the equation = represents electric power flowing into the device, and negative power represents power flowing out.
The formulas hold for either sign convention, unless otherwise noted. Einstein summation convention is used in this article, with vectors indicated by bold font. The connection coefficients of the Levi-Civita connection (or pseudo-Riemannian connection) expressed in a coordinate basis are called Christoffel symbols .
An alternate sign convention is to consider the work performed on the system by its surroundings as positive. This leads to a change in sign of the work, so that = +. This convention has historically been used in chemistry, and has been adopted by most physics textbooks. [25] [27] [28] [29]
In a signed-digit representation, each digit of a number may have a positive or negative sign. In physics, any electric charge comes with a sign, either positive or negative. By convention, a positive charge is a charge with the same sign as that of a proton, and a negative charge is a charge with the same sign as that of an electron.
Radius of curvature sign convention for optical design. Radius of curvature (ROC) has specific meaning and sign convention in optical design. A spherical lens or mirror surface has a center of curvature located either along or decentered from the system local optical axis. The vertex of the lens surface is located on the local optical axis.
Pseudovector – Physical quantity that changes sign with improper rotation; Rotation formalisms in three dimensions – Ways to represent 3D rotations; Right-hand rule – Mnemonic for understanding orientation of vectors in 3D space; Sign convention – Agreed-upon meaning of a physical quantity being positive or negative
This article follows sign-convention # 3, as shown. In the Mohr-circle-space sign convention, normal stresses have the same sign as normal stresses in the physical-space sign convention: positive normal stresses act outward to the plane of action, and negative normal stresses act inward to the plane of action.