In physics, the cross section is a measure of the probability that a specific process will take place when some kind of radiant excitation (e.g. a particle beam, sound wave, light, or an X-ray) intersects a localized phenomenon (e.g. a particle or density fluctuation). For example, the Rutherford cross-section is a measure of probability that an alpha particle will be deflected by a given angle during an interaction with an atomic nucleus. Cross section is typically denoted σ (sigma) and is expressed in units of area, more specifically in barns. In a way, it can be thought of as the size of the object that the excitation must hit in order for the process to occur, but more exactly, it is a parameter of a stochastic process. In classical physics, this probability often converges to a deterministic proportion of excitation energy involved in the process, so that, for example, with light scattering off of a particle, the cross section specifies the amount of optical power scattered from light of a given irradiance (power per area). It is important to note that although the cross section has the same units as area, the cross section may not necessarily correspond to the actual physical size of the target given by other forms of measurement. It is not uncommon for the actual cross-sectional area of a scattering object to be much larger or smaller than the cross section relative to some physical process. For example, plasmonic nanoparticles can have light scattering cross sections for particular frequencies that are much larger than their actual cross-sectional areas. When two discrete particles interact in classical physics, their mutual cross section is the area transverse to their relative motion within which they must meet in order to scatter from each other. If the particles are hard inelastic spheres that interact only upon contact, their scattering cross section is related to their geometric size. If the particles interact through some action-at-a-distance force, such as electromagnetism or gravity, their scattering cross section is generally larger than their geometric size. When a cross section is specified as the differential limit of a function of some final-state variable, such as particle angle or energy, it is called a differential cross section (see detailed discussion below). When a cross section is integrated over all scattering angles (and possibly other variables), it is called a total cross section or integrated total cross section. For example, in Rayleigh scattering, the intensity scattered at the forward and backward angles is greater than the intensity scattered sideways, so the forward differential scattering cross section is greater than the perpendicular differential cross section, and by adding all of the infinitesimal cross sections over the whole range of angles with integral calculus, we can find the total cross section. Scattering cross sections may be defined in nuclear, atomic, and particle physics for collisions of accelerated beams of one type of particle with targets (either stationary or moving) of a second type of particle. The probability for any given reaction to occur is in proportion to its cross section. Thus, specifying the cross section for a given reaction is a proxy for stating the probability that a given scattering process will occur. The measured reaction rate of a given process depends strongly on experimental variables such as the density of the target material, the intensity of the beam, the detection efficiency of the apparatus, or the angle setting of the detection apparatus. However, these quantities can be factored away, allowing measurement of the underlying two-particle collisional cross section. Differential and total scattering cross sections are among the most important measurable quantities in nuclear, atomic, and particle physics. (Wikipedia).
What IS a Cross Section pt. 2: Differential Cross Sections in Particle Physics
Today I discuss how the interpretation of the cross section changes when we both turn on interactions and quantum mechanics. I discuss the importance of the differential cross section in particle physics with a couple examples, including how they can be used as evidence for the existence o
From playlist What is a cross section?
What Exactly IS a Cross Section pt. 1: Cross Sectional Area
Today I I break the world record of longest video explaining cross sectional areas. I spend a good deal of time deriving and giving geometric arguments for the equations most textbooks would simply define for the cross sectional area if one has a single target, or sheet of targets.
From playlist What is a cross section?
A mathematics bonus. In this lecture I remind you of a way to calculate the cross product of two vector using the determinant of a matrix along the first row of unit vectors.
From playlist Physics ONE
The vector cross-product is another form of vector multiplication and results in another vector. In this tutorial I show you a simple way of calculating the cross product of two vectors.
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Physics - Advanced E&M: Ch 1 Math Concepts (7 of 55) What is the Vector Product?
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From playlist PHYSICS 67 ADVANCED ELECTRICITY & MAGNETISM
Calculus 3: Vector Calculus in 3-D (18 of 35) What is a Cross Product?
Visit http://ilectureonline.com for more math and science lectures! In this video I will explain what is a cross product. The cross product of 2 vectors A and B is another vector C and is directed perpendicular to the plane containing A and B. Next video in the series can be seen at: htt
From playlist THE "WHAT IS" PLAYLIST
Calculus 3 Lecture 11.4: The Cross Product
Calculus 3 Lecture 11.4: The Cross Product: Finding the Cross Product of two vectors with Determinants, Using the Cross Product to find Mutually Orthogonal Vectors (with proofs), Torque, Area of a Parallelogram, Volume of a Parallelepiped, and Coplanar Vectors.
From playlist Calculus 3 (Full Length Videos)
Exploring CROSS SECTION Intuitively in GeoGebra 3D with Augmented Reality
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L20.4 Cross section in terms of partial cross sections. Optical theorem
MIT 8.06 Quantum Physics III, Spring 2018 Instructor: Barton Zwiebach View the complete course: https://ocw.mit.edu/8-06S18 YouTube Playlist: https://www.youtube.com/playlist?list=PLUl4u3cNGP60Zcz8LnCDFI8RPqRhJbb4L L20.4 Cross section in terms of partial cross sections. Optical theorem L
From playlist MIT 8.06 Quantum Physics III, Spring 2018
L19.3 Differential and total cross section
MIT 8.06 Quantum Physics III, Spring 2018 Instructor: Barton Zwiebach View the complete course: https://ocw.mit.edu/8-06S18 YouTube Playlist: https://www.youtube.com/playlist?list=PLUl4u3cNGP60Zcz8LnCDFI8RPqRhJbb4L L19.3 Differential and total cross section License: Creative Commons BY-N
From playlist MIT 8.06 Quantum Physics III, Spring 2018
Lec 2 | MIT 22.091 Nuclear Reactor Safety, Spring 2008
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From playlist MIT 22.091 Nuclear Reactor Safety, Spring 2008
Alejandro Rodriguez - Physical bounds on wave phenom as quadratically constrained quadratic programs
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Astrophysical neutrinos by Subhendu Rakshit
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From playlist Celebrating the Science of Giorgio Parisi (ONLINE)
L21.2 Phase shifts and impact parameter
MIT 8.06 Quantum Physics III, Spring 2018 Instructor: Barton Zwiebach View the complete course: https://ocw.mit.edu/8-06S18 YouTube Playlist: https://www.youtube.com/playlist?list=PLUl4u3cNGP60Zcz8LnCDFI8RPqRhJbb4L L21.2 Phase shifts and impact parameter License: Creative Commons BY-NC-S
From playlist MIT 8.06 Quantum Physics III, Spring 2018
MIT 22.01 Introduction to Nuclear Engineering and Ionizing Radiation, Fall 2016 Instructor: Michael Short View the complete course: https://ocw.mit.edu/22-01F16 YouTube Playlist: https://www.youtube.com/playlist?list=PLUl4u3cNGP61FVzAxBP09w2FMQgknTOqu The full, seven-dimensional neutron t
From playlist MIT 22.01 Introduction to Nuclear Engineering and Ionizing Radiation, Fall 2016