Two coils N1 and N2 turns are wound concentrically on a straight cylindrical core of radius r and permeability μ. The windings have lengths l1 and l2 respectively as shown in the figure. The mutual inductance will be1. Proportional to N1 N2.2. Proportional to μ 3. Inversely proportional to l1.4. Inversely proportional to r2Which of these statements are correct?

• A. 1, 2, 3 and 4
• B. 2, 3 and 4 only
• C. 1, 2 and 3 only
• D. 1, 3 and 4 only