GKFix MCQ Question

What is the self-inductance of a long solenoid with a magnetic core of relative permeability μ_r?

• A. L = μ_0 n A l
• B. L = μ_r μ_0 n A / l
• C. L = μ_r μ_0 n² A l
• D. L = μ_0 n² A / l