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77julia77 [94]
3 years ago
9

A current I flows down a wire of radius a.

Physics
1 answer:
Helga [31]3 years ago
7 0

Answer:

(a) K = \frac{I}{2\pi a}

(b) J = \frac{I}{2\pi as}

Explanation:

(a) The surface current density of a conductor is the current flowing per unit length of the conductor.

                                   K = \frac{dI}{dL}

Considering a wire, the current is uniformly distributed over the circumferenece of the wire.

                                   dL = 2\pi r

The radius of the wire = a

                                    dL = 2\pi a

The surface current density K = \frac{I}{2\pi a}

(b) The current density is inversely proportional

                                     J \alpha  s^{-1}    

                                     J = \frac{k}{s}           ......(1)

k is the constant of proportionality

                                     I = \int\limits {J} \, dS

                                     I = J \int\limits \, dS     ........(2)

substituting (1) into (2)

                                     I = \frac{k}{s} \int\limits\, dS

                                     I = k \int\limits^a_0 \frac{1}{s}  {s} \, dS

                                     I = 2\pi k\int\limits\, dS

                                     I = 2\pi ka

                                     k = \frac{I}{2\pi a}

substitute J = \frac{k}{s}

                                     J = \frac{I}{2\pi as}

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