# Solved Problem-5

Problem-5

A transmission line consists of a pair of long parallel conductors of radius

*r*with a spacing*D*between centres in a medium of permittivity*Îµ*. Show that when*D*is large compared to*r*, the capacitance of the pair of conductors per unit length is given approximately by,Solution

We consider a line charge distribution of density

*Î»*between the two cylindrical conductors. If the charge on the conductor*A*is positive, it will be negative on the conductor*B*by electrostatic induction.**Capacitance between two wire transmission lines**

The electric field intensity at the point

*P*is due to both the charges and is written as,The potential at

Hence, the capacitance of the pair of conductors per unit length is given as,

*P*is given as,