Calculate the time constant of a straight solenoid of length l = 1.0 m having a single-layer

Question:

Calculate the time constant τ of a straight solenoid of length l = 1.0 m having a single-layer winding of copper wire whose total mass is equal to m =1.0 kg. The cross-sectional diameter of the solenoid is assumed to be considerably less than its length. Note. The time constant τ is the ratio L/R, where L is inductance and R is active resistance.