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Estimation of the Physical Quantities

Estimation of the Physical Quantities

On many occasions, physicists, other scientists, and engineers need to make estimates of a particular quantity. These are sometimes referred to as guesstimates, order-of-magnitude approximations, back-of-the-envelope calculations, or Fermi calculations. The physicist Enrico Fermi was famous for his ability to estimate various kinds of data with surprising precision. Estimating does not mean guessing a number or a formula at random. Instead, estimation means using prior experience and sound...

Gauss's Law: Planar Symmetry

Gauss's Law: Planar Symmetry

A planar symmetry of charge density is obtained when charges are uniformly spread over a large flat surface. In planar symmetry, all points in a plane parallel to the plane of charge are identical with respect to the charges. Suppose the plane of the charge distribution is the xy-plane, and the electric field at a space point P with coordinates (x, y, z) is to be determined. Since the charge density is the same at all (x, y) - coordinates in the z = 0 plane, by symmetry, the electric field at P...

Electric Field of a Non Uniformly Charged Sphere

Electric Field of a Non Uniformly Charged Sphere

Gauss's law states that the electric flux through any closed surface equals the net charge enclosed within the surface. This law is beneficial for determining the expressions for the electric field for a particular charge distribution if the electric flux is known.
Consider a non-uniformly charged sphere, for which the density of charge depends only on the distance from a point in space and not on the direction. Such a sphere has a spherically symmetrical charge distribution. Here, the electric...

Gauss's Law: Spherical Symmetry

Gauss's Law: Spherical Symmetry

A charge distribution has spherical symmetry if the density of charge depends only on the distance from a point in space and not on the direction. In other words, if the system is rotated, it doesn't look different. For instance, if a sphere of radius R is uniformly charged with charge density ρ0, then the distribution has spherical symmetry. On the other hand, if a sphere of radius R is charged so that the top half of the sphere has a uniform charge density ρ1 and the bottom half has a uniform...

Plane Electromagnetic Waves II

Plane Electromagnetic Waves II

Consider a plane wavefront traveling in position x-direction with a constant speed. This wavefront can be utilized to obtain the relationship between electric and magnetic fields with the help of Faraday's law.

Electric Field of Two Equal and Opposite Charges

Electric Field of Two Equal and Opposite Charges

Atoms generally contain the same number of positively and negatively charged particles, protons, and electrons. Hence, they are electrically neutral. However, the centers of the positive and negative charges do not always coincide. In such a scenario, the electric field of an atom may not be zero.
A separation of the positive and negative charges can lead to a weak, remnant effect of the positive and negative charges. The expectation is that the more the distance between the positive and...

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Related Experiment Video

Updated: May 25, 2026

Scattering And Absorption of Light in Planetary Regoliths

Scattering And Absorption of Light in Planetary Regoliths

Published on: July 1, 2019

[Estimation of the phantom scatter factor (Sp) of rectangular fields].

Takahide Hayakawa¹, Takumi Yamada, Hironori Sakai

¹Department of Medical Radiation Technology, School of Health Sciences, Niigata University.

Nihon Hoshasen Gijutsu Gakkai Zasshi

|January 27, 2012

Summary

This study introduces a new method to accurately calculate the phantom scatter factor (Sp) for any rectangular radiation field. The area ratio correction method improves accuracy over existing techniques for radiation therapy dose calculations.

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Last Updated: May 25, 2026

Scattering And Absorption of Light in Planetary Regoliths

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In situ Grazing Incidence Small Angle X-ray Scattering on Roll-To-Roll Coating of Organic Solar Cells with Laboratory X-ray Instrumentation

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Published on: September 8, 2016

Area of Science:

Medical Physics
Radiation Oncology

Context:

Accurate dose calculation is crucial in radiation therapy.
The phantom scatter factor (Sp) is a key parameter for determining dose.
Estimating Sp for non-square fields presents a challenge.

Purpose:

To develop and validate a method for accurately estimating the phantom scatter factor (Sp) for arbitrary rectangular radiation fields.
To compare the accuracy of a novel equivalent square calculation method (area ratio correction) with conventional methods.

Summary:

Output doses were measured for various field sizes using 4 MV and 10 MV X-rays.
Equations for Sp on square fields were derived, incorporating primary dose and scatter components.
A new area ratio correction method for equivalent squares was found to be more accurate than Bjärngard's method for rectangular fields.

Impact:

Enables more precise dose calculations in radiation therapy for non-standard rectangular fields.
Improves the accuracy of treatment planning systems.
Contributes to enhanced patient safety and treatment efficacy in radiotherapy.