DC coil current: An 18 V supply is connected across a coil with winding resistance 180 Ω (ignore inductance at steady state). What is the current?

Introduction / Context:Once steady state is reached in a DC circuit, an inductor behaves as a short circuit and only its winding resistance limits current. This is a direct application of Ohm's law.

Given Data / Assumptions:

• Supply voltage V = 18 V (DC).
• Winding resistance R = 180 Ω.
• Steady state, so inductive reactance is zero.

Concept / Approach:

Use Ohm's law I = V / R at steady state. The inductive element does not impede DC after transients decay.

Step-by-Step Solution:

Verification / Alternative check:

If the transient were considered, current would rise exponentially from 0 A to 100 mA with time constant τ = L/R. At t → ∞, the value is 100 mA as computed.

Why Other Options Are Wrong:

1 mA and 10 mA are too small by factors of 100 and 10 respectively. 1 A would require only 18 Ω of resistance, not 180 Ω.

Common Pitfalls:

Applying AC reactance to a DC steady-state question; forgetting that inductors pass DC after transients.

Final Answer:

100 mA