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Long Cubit

The long cubit is an ancient unit of length that is a variation of the standard cubit, measuring from the elbow to the tip of the middle finger. The long cubit is longer than the common cubit, typically about 21 inches (approximately 53 centimeters).

It was used in ancient civilizations such as Egypt and Mesopotamia for construction, land measurement, and crafts, especially when more precision or a larger unit was needed.

Key points:

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  Long cubit ≈ 21 inches (53 cm)

  
  
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  Longer than the standard cubit (usually about 18 inches)

  
  
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  Used in ancient architecture and surveying

  
  
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  Provided a larger base unit for measurements in construction

  
  

The long cubit helped ancient builders and surveyors manage larger scales while still relying on the human body as a reference.

Classical Electron Radius

The classical electron radius is a theoretical length scale associated with the electron, derived from classical electromagnetism. It represents the size of a hypothetical sphere where the electron’s electrostatic energy equals its rest mass energy.

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  Its value is approximately 2.818 × 10⁻¹⁵ meters (about 2.8 femtometers).

  
  
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  Calculated using fundamental constants: the electron charge, mass, and the speed of light.

  
  
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  It is not the actual physical size of the electron (which is considered point-like in quantum mechanics), but a useful scale in classical physics.

  
  
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  Used in scattering theory and classical electron models.

  
  

Key facts:

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  Classical electron radius ≈ 2.818 × 10⁻¹⁵ m

  
  
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  Represents an electromagnetic length scale, not a physical size

  
  
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  Important in classical models of electron behavior

  
  

This radius helps bridge classical and quantum views of particle physics.