The time constant of inductance coil is 3 ~m ~s . When a 90 resistance is joined in series, then the time constant becomes 0.5 ~m ~s . The inductance and the resistance of the coil are

Step-by-step solution

Time constant t= L R 3= L R ...(i) When a 90 resistance is joined in series the time constant becomes 0.5 ~m ~s . So, 0.5= L R+90 ...(ii) From Eqs. (i) and (ii) 3 10⁻³ 0.5 10⁻³ = R+90 R 30 5 = R+90 R 6 R=R+90R=18 This value put in Eq. (i) 3 10⁻³= L R 3 10⁻³= L 18 or L=54 mH