Question 1 [20 marks] (a)[5 marks] List the two observations that lead to the two fundamental postulates of the electrostatic field and discuss their implications in the integration forms. (b)[15 marks] A coaxial cable operates at 66 kV and the inner conductor diameter is 2 cm. The cable has two insulating layers: rubber with relative dielectric constant &,, =4, dielectric breakdown strength = 25MV/m and polystyrene with relative dielectric constant &rp = 2.5, the dielectric breakdown strengths 20 MV/m (i) [3 marks] Which dielectric should be selected for the inner layer and why? (ii)[12 marks] Calculate the thickness of the two insulation layers so that the maximum electric field intensities will not exceed 25% of the respective breakdown levels. Consider outside of the outer layer insulation is at ground potential.

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