11. (8 %) Assume a uniformly wound solenoid having N turns and length ℓ, and ℓ is much greater than the radius of the solenoid, prove: (a) the flux through each turn of area A is ΦB = μB NIA / ℓ, and (b) the inductance is L = μ_B N² A / ℓ. Your proofs for (a): __(11a) (4%)__ and for (b)__ (11b) (4%)__