- #1
avicenna
- 84
- 8
What is the value of the permeability constant in 1865, the time when Maxwell's theory was first published? What was the experimental method used to determine the constant. Who did the experiment.
Nothing there.anorlunda said:I'm not sure. Try reading the papers linked in this article.
https://en.wikipedia.org/wiki/Oliver_Heaviside
OK. The original derivation of radiation speed is too difficult for me. I don't really know how our modern EM speed derivation may be related or compared to Maxwell's original.jtbell said:Maxwell didn't actually use the equation ##v = \frac 1 {\sqrt {\mu_0 \epsilon_0}}##. That equation uses SI units which hadn't been codified in Maxwell's day. He used a different set of units, and indeed different names for many electromagnetic quantities. The equation we use nowadays should be considered a modern "translation" or "interpretation" of Maxwell's calculations. For what it's worth, you can see what Maxwell actually wrote when he calculated the theoretical speed of his electromagnetic waves:
https://en.wikisource.org/wiki/Page:Philosophical_magazine_23_series_4.djvu/38
In the cgs system in use at that time (and also when I was at school) there are two sets of units, emu and esu. The emu is current (charge x velocity) necessary to produce a force of 1 dyne between two conductors, and the esu is the charge necessary to produce a force of 1 dyne between two charges, all spaced 1cm. For a vacuum, permeability and permittivity were defined as 1. Maxwell noticed that the ratio of these two units was about equal to 3 x 10^8 m/s, which is c.avicenna said:OK. The original derivation of radiation speed is too difficult for me. I don't really know how our modern EM speed derivation may be related or compared to Maxwell's original.
Great! Very helpful. Though I don't understand it now, this is the hint if I want to investigate further. I do know that the force between currents in conductors is related to the magnetic field and thus to permeability. The other is simply related to permittivity.tech99 said:In the cgs system in use at that time (and also when I was at school) there are two sets of units, emu and esu. The emu is current (charge x velocity) necessary to produce a force of 1 dyne between two conductors, and the esu is the charge necessary to produce a force of 1 dyne between two charges, all spaced 1cm. For a vacuum, permeability and permittivity were defined as 1. Maxwell noticed that the ratio of these two units was about equal to 3 x 10^8 m/s, which is c.
The permeability constant, also known as the magnetic constant or vacuum permeability, is a physical constant that describes the strength of the magnetic field in a vacuum. It is denoted by the symbol μ0 and has a value of approximately 4π×10-7 newtons per ampere squared (N/A2).
The value of the permeability constant can be measured using a device called a magnetometer, which measures the strength of a magnetic field. It can also be calculated by measuring the force between two current-carrying wires and using the equation μ0 = 4π×10-7 N/A2.
The permeability constant is important because it is used in many equations that describe the behavior of magnetic fields. It is also a fundamental constant in physics and plays a crucial role in understanding the properties of matter and electromagnetism.
The value of the permeability constant has not changed over time. It is a fundamental constant of nature and is considered to be a fixed value. However, advances in technology and measurement techniques have led to more precise measurements of the constant.
In 1865, the value of the permeability constant was not yet known. It was first accurately measured in 1883 by the German physicist Heinrich Hertz and has remained the same since then. However, earlier estimates of the constant by scientists such as James Clerk Maxwell and Lord Kelvin were only slightly off from the currently accepted value.