AP EAPCET 19-Aug-2021 Shift 2 Paper

Length of solenoid, l1=60×cm=60×10−2m
Turns per cm(n1) and (n2) are 1500 turns/m and 4000 turns/m.
For 1 st solenoid, area of cross-section, A1=4×10−3m2
For 2 nd solenoid, area of cross section, A2=2×10−3m2
∵ Mutual inductance is same. (i.e., M12=M21=M )
∴M=(µ0n1n2A2l)
=4π×10−7×1500×4000×2×10−3×60×10−2
=9.04×10−3=9.04‌mH≃9‌mH