Question

when t<0, the switch is closed, and the inductor acts as a short circuit to dc. The 16-Ω resistor is short-circuited; we combine the 4-Ω and 12-Ω resistors in parallel

Answer 1

However, in the real world “ALL” coils whether they are chokes, solenoids, relays or any wound component will always have a certain amount of resistance no matter how small. This is because the actual coils turns of wire being used to make it uses copper wire which has a resistive value.

Then for real world purposes we can consider our simple coil as being an “Inductance”, L in series with a “Resistance”, R. In other words forming an LR Series Circuit.

A LR Series Circuit consists basically of an inductor of inductance, L connected in series with a resistor of resistance, R.

Explanation:

i hope this will help.