## What is the cross section of a molecule?

The collisional cross section is defined as the area around a particle in which the center of another particle must be in order for a collision to occur. In the image below, the area within the black circle is molecule A’s collisional cross section.

What is an extinction cross section?

(Also called attenuation cross section, especially for radar and radio wave propagation.) The area that, when multiplied by the irradiance of electromagnetic waves incident on an object, gives the total radiant flux scattered and absorbed by the object.

### What is cross section in nuclear physics?

Cross section, in nuclear or subatomic particle physics, probability that a given atomic nucleus or subatomic particle will exhibit a specific reaction (for example, absorption, scattering, or fission) in relation to a particular species of incident particle.

Can absorption cross section negative?

When refractive index is just a number, then scattering cross-section is positive and absorption cross-section is zero. Negative extinction cross-section means pumping or a gain medium.

#### What is cross section in spectroscopy?

Absorption cross section is a measure for the probability of an absorption process. More generally, the term cross section is used in physics to quantify the probability of a certain particle-particle interaction, e.g., scattering, electromagnetic absorption, etc.

What is the formula of collision frequency?

In every cylindrical collision volume Vc=σ⋅λ there is by definition just one particle, namely the particle with which the moving particle collides. Then the moving particle will change its direction and define a new collision volume, again with a “target” particle with which it will collide.

## What is cross section plan?

A cross section, also simply called a section, represents a vertical plane cut through the object, in the same way as a floor plan is a horizontal section viewed from the top. A sectional elevation is a combination of a cross section, with elevations of other parts of the building seen beyond the section plane.

What is uniform cross section?

Uniform means identical, or exactly the same, and a cross section is when you cut an object in half and reveal the shape inside. So a uniform cross section is when you cut an object straight through, and the resulting shape inside matches the bases, or ends, of the shape exactly.

### How is nuclear cross section measured?

The concept of a nuclear cross section can be quantified physically in terms of “characteristic area” where a larger area means a larger probability of interaction. The standard unit for measuring a nuclear cross section (denoted as σ) is the barn, which is equal to 10−28 m², 10−24 cm² or 100 fm².

What is cross section in electric current?

Cross section represents a plane made by cutting across something at right angles to its length. If you cut a wire and look straight on you will see a circular plate.

#### What is absorption cross section in laser?

How is the absorption cross section used in physics?

Absorption cross section is a measure for the probability of an absorption process. More generally, the term cross section is used in physics to quantify the probability of a certain particle-particle interaction, e.g., scattering, electromagnetic absorption, etc. (Note that light in this context is described as consisting of particles, i.e.,

## Why is the absorption cross section called the GM?

(Note that light in this context is described as consisting of particles, i.e., photons.) In honor of the fundamental contribution of Maria Goeppert Mayer to this area, the unit for the two-photon absorption cross section is named the “GM”.

Which is the correct description of the absorption spectrum?

The initial and final states are bound (or quasibound) and the absorption spectrum consists of sharp (or slightly broadened, but in principle resolvable) lines, as described in Section 6.1.1. 2.

### How is the absorption rate related to the Golden Rule?

Now let’s relate the rates of absorption to a quantity that is directly measured, an absorption cross section α: α = total energy absorbed per unit time total incident intensity (energy/unit time/area) = ℏωwkℓ I Note α has units of cm 2 . The golden rule rate for absorption also gives the same rate for stimulated emission.