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Cylindrical capacitor
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Capacitance per unit length of coaxial cable.
C/L = 2πε₀/ln(b/a)Coaxial cylinders have C/L = 2πε₀/ln(b/a), the model for coaxial cables.
a = 1 mm, b = 3 mm: about 51 pF/m.
Edge effects ignored.
In more detail
A cylindrical capacitor has two coaxial cylinders, with capacitance per unit length C/L = 2πε0 / ln(b/a). It is the basis of coaxial cables.
Real-world uses
- Coaxial cables have this geometry to shield signals.
- Calculating capacitance of cable lengths in telecommunications.
- Engineers use the capacitance per unit length of coaxial cable to calculate signal loss and timing in cables.
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Frequently asked questions
Why is it per unit length?
Because the capacitance depends on the length of the cylinders.
What does b/a mean?
The ratio of outer to inner radius, which sets how strongly the field spreads.
Why does coaxial cable have this shape?
The inner conductor and outer shield keep the field inside the cable, reducing interference with the outside world.
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