Physics

Physics

Problem

In terms of resistance RR and time TT, what are the dimensions of the ratio μϵ\frac{\mu}{\epsilon} of the permeability μ\mu and permittivity ϵ\epsilon? a. [RT−2][RT^{-2}] b. [R2T−1][R^2T^{-1}] c. [R2][R^2] d. [R2T2][R^2T^2]
Intuitive explanation

The key insight is that μ\mu and ϵ\epsilon appear together in the wave equation for electromagnetic waves, where their product determines the speed of light: c=1/μϵc = 1/\sqrt{\mu\epsilon}. By rearranging this relationship and using the fact that resistance has dimensions of [ML2T−3I−2][ML^2T^{-3}I^{-2}] and speed has dimensions of [LT−1][LT^{-1}], you can express the ratio μ/ϵ\mu/\epsilon in terms of RR and TT. The trick is recognizing that impedance (which has dimensions of resistance) naturally connects electromagnetic properties to mechanical quantities.

Intuitive explanation

The key insight is that μ\mu and ϵ\epsilon appear together in the wave equation for electromagnetic waves, where their product determines the speed of light: c=1/μϵc = 1/\sqrt{\mu\epsilon}. By rearranging this relationship and using the fact that resistance has dimensions of [ML2T−3I−2][ML^2T^{-3}I^{-2}] and speed has dimensions of [LT−1][LT^{-1}], you can express the ratio μ/ϵ\mu/\epsilon in terms of RR and TT. The trick is recognizing that impedance (which has dimensions of resistance) naturally connects electromagnetic properties to mechanical quantities.

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