- × or x or X
- the usual symbol for power as a unit of
magnification. More generally, × or x is used with its
mathematical meaning, "times," to indicate
that a measurement is a multiple of some standard or reference measurement.
For example, an image marked 200× is shown at 200 times actual size (that
is, distances are 200 times actual size), and a 10x CD-ROM drive is one
capable of transferring data 10 times faster than the "normal" or standard
- X unit (Xu)
- a unit of distance formerly used for measuring the wavelength
of x-rays and gamma rays. The X unit is approximately 1.0021 x
10-13 meter, 0.001 0021 angstrom,
or 100.21 femtometers. The wavelength of these powerful forms of
radiation is now measured in picometers (pm) or femtometers (fm).
The unit was defined by the Swedish physicist K. M. G. Siegbahn in
1925, at a time when the wavelengths could not be measured
directly. The definition was made in terms of the spacing between
planes of the calcite crystals used in the measuring apparatus.
Siegbahn, who received the Nobel Prize in Physics in 1924 for his
work in X-ray spectroscopy, aimed to define a unit equal to
approximately 10-13 meter, and he succeeded admirably.
In his honor the unit was also called the Siegbahn
Return to the Dictionary Contents
Skip to: A B
C D E
F G H
I J K
L M N
O P Q
R S T
U V W
X Y Z
You are welcome to email
the author (email@example.com) with comments and
All material in this folder is copyright © 2000 by Russ
Rowlett and the University of North Carolina at Chapel Hill.
Permission is granted for personal use and for use by individual
teachers in conducting their own classes. All other rights reserved.
You are welcome to make links to this page, but please do not copy
the contents of any page in this folder to another site. The material
at this site will be updated from time to time.
March 17, 2000