\Eta
The Greek letter Eta (\Eta) is used in various scientific and mathematical contexts. In physics, it often represents efficiency or viscosity. In mathematics, it can denote a function or a variable, depending on the context.
Represents efficiency in physics, where \Eta is the efficiency ratio.
\Eta = \frac{\text{useful output}}{\text{total input}}
Represents viscosity in fluid dynamics, where \Eta is the dynamic viscosity.
\Eta = \frac{F}{A}
Used as a variable in an integral, where \Eta is a constant parameter.
\int_0^\infty e^{-\Eta x} \, dx