NCERT Physics Class 12 Exemplar Ch 8 Electromagnetic Waves Part 4

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Long Answer

Q 28 An infinitely long thin wire carrying a uniform linear static charge density λ is placed along the z-axis (Figure). The wire is set into motion along its length with a uniform velocity. Calculate the Poynting vector

infinitely long thin wire carrying a uniform linear

Infinitely Long Thin Wire Carrying a Uniform Linear


Q 29 Sea water at frequency Hz has permittivity, permeability μ ≈ μo and resistivity. Imagine a parallel plate capacitor immersed in sea water and driven by an alternating voltage source what fraction of the conduction current density is the displacement current density?


Let the distance between the plates be d. Then the electric field

The conduction current density is given by the Ohm’s.


The displacement current density is given as

Q 30 A long straight cable of length is placed symmetrically along z-axis and has radius the cable consists of a thin wire and a co-axial conducting tube. An alternating current I flows down the central thin wire and returns along the co-axial conducting tube. The induced electric field at a distance s from the wire inside the cable is

(i) Calculate the displacement current density inside the cable.

(ii) Integrate the displacement current density across the cross-section of the cable to find the total displacement current Id.

(iii) Compare the conduction current with the displacementcurrent .


(i) Displacement curing density can be found from the relation be


iii) The displacement current

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