A certain transmission line (very long) is constructed from two thin metal plates (parallel to each other) of width b, which are separated by a very small distance ‘h’ << ‘b’ . The current travels down one strip and back along the other, and it is distributed uniformly over the surface of the plates as shown in figure. Neglect fringing field at ends of plates.

Capacitance per unit length of this combination is

Options

A. infinite
B. `(epsilon_(0)h^(2))/b`
C. `(epsilonb^(2))/(h^(2))`
D. `(epsilon_(0)b)/h`

Explanation

Considering length of line is
`E=(sigma)/(epsilon_(0))rArr V=Eh`
`V=(sigma)/(epsilon_(0))h=Q/(epsilon_(0)bl).h=c=Q/v`
`C=(epsilon_(0)bl)/h`
`C/l=(epsilon_(0)b)/h`
`rArr B=(mu_(0)K)/2+(mu_(0)K)/2=mu_(0)K=(mu_(0)I)/b` (K=current per unit width)
`vec(B)=(mu_(0)I)/b(-hatk)`

Consider a rectangular surface as shown in the figure.
Now `phi=Bvl`
`phi=(mu_(0)I)/b.h l =LI`
`L=(mu_(0)hl)/b`
`L/l=(mu_(0)h)/b` BUt
`c=1/(sqrt(mu_(0)epsilon_(0)))`
`c^(2)=1/(sqrt(mu_(0)epsilon_(0)))`
`mu_(0)=1/(epsilon_(0)c^(2))`
`L/l=h/(epsilon_(0)c^(2)b)`