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Glossary O

Ockham’s Razor
A premise in the philosophy of science
due to William of Ockham which states that “entities should not
be multiplied unnecessarily.” This is commonly interpreted to
mean that the simplest of a set of competing viable theories is
preferable.
Olber’s Paradox
If the universe has an infinite amount
of stars then the sky should be infinitely bright. But many stars
have been born, lived, and died already. Basically at any one
time there are not enough stars active to fill the space of the
Universe with enough radiation to light the night sky so therefore
the sky is dark at night. [more]
Optical Activity
A material is optically active if it
rotates the plane of polarisation of any light transmitted through
it. It is a property found in sugars and some other naturally
occurring compounds and was first observed by the French physicist
D. Arago, in 1811. There are two types of optically active materials;
those that rotate the plane of polarization to the right (clockwise
as one looks along the beam of light) are called dextrorotatory
(right-handed), and those that rotate the plane to the left (counterclockwise)
are called levorotatory (left-handed). A device for measuring
optical activity is called a polarimeter. [more]
Oort Cloud
The Oort cloud is a postulated cloud
of comets situated about 50,000 to 100,000 AU from the sun. Although
no direct observations have been made of such a cloud, it is believed
to be the source of most or all comets entering the inner solar
system (some short-period comets may come from the Kuiper belt),
based on observations of the orbits of comets.
Oscilloscope
The oscilloscope is an electronic instrument
widely used in making electrical measurements. The main component
of the oscilloscope is the cathode ray tube (CRT). The CRT is
a vacuum tube in which electrons are accelerated and deflected
under the influence of electric field. The electrons are deflected
in various directions by two sets of plate placed at right angle
to each other in the neck of the tube. Signal for the horizontal
deflection plate (X-axis) is generated by the scope [Virtual
Scope]
Order of magnitude
An estimate of the size of something
expressed to the nearest power of ten for example the radius of
atom is 10-15, this is an estimate.
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