A sensitive electronic device of resistance 175Ω is to be connected to a source of emf by a switch. The device is designed to operate with a current of 36 mA, but to avoid damage to the device, the current can rise to no more than 4.9 mA in the first 58μs after the switch is closed. To protect the device it is connected in series with an inductor.
a. What emf must the source have?
b. What inductance is required?
c. What is the time constant?