Bispherical coordinates
From Wikipedia, the free encyclopedia
Bispherical coordinates are a three-dimensional orthogonal coordinate system that results from rotating the two-dimensional bipolar coordinate system about the axis that connects the two foci. Thus, the two foci F1 and F2 in bipolar coordinates remain points (on the z-axis, the axis of rotation) in the bispherical coordinate system.
Contents |
[edit] Definition
The most common definition of bispherical coordinates (σ,τ,φ) is
where the σ coordinate of a point P equals the angle F1PF2 and the τ coordinate equals the natural logarithm of the ratio of the distances d1 and d2 to the foci
[edit] Coordinate surfaces
Surfaces of constant σ correspond to intersecting tori of different radii
that all pass through the foci but are not concentric. The surfaces of constant τ are non-intersecting spheres of different radii
that surround the foci. The centers of the constant-τ spheres lie along the z-axis, whereas the constant-σ tori are centered in the xy plane.
[edit] Inverse formulae
[edit] Scale factors
The scale factors for the bispherical coordinates σ and τ are equal
whereas the azimuthal scale factor equals
Thus, the infinitesimal volume element equals
and the Laplacian is given by
Other differential operators such as and can be expressed in the coordinates (σ,τ) by substituting the scale factors into the general formulae found in orthogonal coordinates.
[edit] Applications
The classic applications of bispherical coordinates are in solving partial differential equations, e.g., Laplace's equation or the Helmholtz equation, for which bispherical coordinates allow a separation of variables. A typical example would be the electric field surrounding two conducting spheres of different radii.
[edit] See also
- Orthogonal coordinates
- Two dimensional orthogonal coordinate systems
- Three dimensional orthogonal coordinate systems
- Elliptic cylindrical coordinates
- Toroidal coordinates
- Bispherical coordinates
- Bipolar cylindrical coordinates
- Conical coordinates
- Flat-Ring cyclide coordinates
- Flat-Disk cyclide coordinates
- Bi-cyclide coordinates
- Cap-cyclide coordinates
[edit] References
[edit] Bibliography
- Morse PM, Feshbach H (1953). Methods of Theoretical Physics, Part I. New York: McGraw-Hill, pp. 665–666.
- Korn GA, Korn TM (1961). Mathematical Handbook for Scientists and Engineers. New York: McGraw-Hill, p. 182. LCCN 59-14456.
- Zwillinger D (1992). Handbook of Integration. Boston, MA: Jones and Bartlett, p. 113. ISBN 0-86720-293-9.
- Moon PH, Spencer DE (1988). "Bispherical Coordinates (η, θ, ψ)", Field Theory Handbook, Including Coordinate Systems, Differential Equations, and Their Solutions, corrected 2nd ed., 3rd print ed., New York: Springer Verlag, pp. 110–112 (Section IV, E4Rx). ISBN 0-387-02732-7.