8. The secondary rms voltage of an ignition transformer in a furnace is 10.0 kV. When the primary operates at an rms voltage of 120 V, the primary impedance is 24.0 0 and the transformer is 90% efficient. a. What turns ratio is required? b. What is the current in the secondary? c. What is the impedance in the secondary? 9. A 12.6-V battery is connected in series with a 30.0-mH inductor, a 0.150-0 resistor, and a switch. The switch is closed at time t = 0. a. Find the time constant of the circuit. b. Find the current after one time constant. c. Find the voltage drop across the resistor at t = 0 and t = T. d. What's the rate of change of current after one time constant? e. Find the time required for the current to reach 99.9% of its maximum value