Electromagnetic Waves — Important Questions

2.25

Use v = c / sqrt(μr εr). Rearranging gives εr = c²/(v² μr). Substituting c = 3.0 × 10^8 m/s, v = 2.0 × 10^8 m/s, μr = 1.0, we get εr = (3.0²)/(2.0²) = 9/4 = 2.25.

4.0 × 10^-7 T

Use E/B = c, so B0 = E0/c = 120 / (3.0 × 10^8) = 4.0 × 10^-7 T.

4.77 × 10^-2 W m^-2

Use ⟨I⟩ = 1/2 ε0 E0² c. Substituting ε0 = 8.85 × 10^-12, E0 = 60 N/C, c = 3.0 × 10^8 m/s gives ⟨I⟩ = 0.5 × 8.85 × 10^-12 × 3600 × 3.0 × 10^8 = 4.77 × 10^-2 W m^-2.

Ic = 0 and Id = 0

When the capacitor is fully charged, no current flows in the wires and the electric field between the plates is no longer changing. Therefore both conduction current and displacement current become zero.