Physically used to represent magnetic flux or electric potential. The lowercase form is φ.

In the function y=asin(ωx+φ), it represents the translation size from left to right.

In engineering, φ represents the diameter of cylindrical material equipment. For example, φ 10 is 10 unit diameters.

In physics, the focal length is expressed by φ.

Glasses degree = 1/φ

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