Resistor behavior in RL circuits — is the voltage across a pure resistor always out of phase with current?

Introduction / Context:
Phase relations differ across R, L, and C. Even within an RL network, the voltage across the resistor element itself follows the basic rule for pure resistors. This question checks whether the presence of an inductor changes the in-phase relationship at the resistor terminals.

Given Data / Assumptions:

• Ideal resistor R has voltage and current in phase.
• RL network is driven by a sinusoidal source.
• Voltage measured specifically across the resistor element.

Concept / Approach:
For a pure resistor, Ohm’s law gives V_R = I_R * R with R real and frequency independent. Therefore, phase(V_R) equals phase(I_R). Although the total circuit current lags the source voltage in an RL network, that lag applies to the current through both elements. The resistor’s voltage is exactly aligned with that current, not shifted by ±90 degrees as in reactive elements.

Step-by-Step Solution:

Verification / Alternative check:
On a scope, compare the resistor’s voltage waveform to a current-sense signal. Peaks line up with no time shift beyond measurement error, confirming zero phase difference across the resistor.

Why Other Options Are Wrong:

• Answering “True” confuses the total circuit phase lag (current versus source voltage) with the local element relationship at the resistor, which remains in phase by definition.

Common Pitfalls:
Assuming that the presence of reactive elements changes the intrinsic resistor relationship. Only the inductor and capacitor introduce ±90 degree shifts between their own voltage and current.

Final Answer:
False