GKFix MCQ Question

For two solenoids, what is the mutual inductance if the medium has relative permeability µr?

• A. M = µ₀ n₁ n₂ π r₁² l
• B. M = µr µ₀ n₁ n₂ π r₁² l
• C. M = µ₀ n₁ n₂ π r₂² l
• D. M = µr µ₀ n₁ n₂ π r₂² l