Loaded voltage divider — consider attaching different loads to the same divider output. Which statement is more accurate: connecting a 6 kΩ load will cause a smaller drop in the divider's output voltage than connecting a 5 kΩ load (since 6 kΩ loads the source less)?

Difficulty: Easy

Correct Answer: Correct

Explanation:


Introduction / Context:
A voltage divider provides a reference voltage but is sensitive to loading. When an external load is connected, the output falls due to the divider's Thevenin resistance. This question compares two loads (6 kΩ versus 5 kΩ) to evaluate which causes less output sag.


Given Data / Assumptions:

  • Same divider and same open-circuit output V_oc for both cases.
  • Load options: 6 kΩ and 5 kΩ connected to the divider output node.
  • Linear, time-invariant resistors; DC or low-frequency behavior; source internal resistance may be modeled as part of the Thevenin resistance R_th.


Concept / Approach:
The loaded output is V_out = V_oc * (R_L / (R_th + R_L)). For fixed R_th and V_oc, a larger R_L yields a larger fraction and therefore a higher V_out (less droop). Hence, 6 kΩ (larger than 5 kΩ) loads the divider less and produces a smaller decrease from the open-circuit value.


Step-by-Step Solution:

Model the divider and its source as a Thevenin equivalent: V_oc in series with R_th.For R_L = 6 kΩ: V6 = V_oc * (6k / (R_th + 6k)).For R_L = 5 kΩ: V5 = V_oc * (5k / (R_th + 5k)).Compare: since 6k / (R_th + 6k) > 5k / (R_th + 5k) for R_th ≥ 0, V6 > V5, so the 6 kΩ load causes a smaller drop.


Verification / Alternative check:
Pick R_th = 2 kΩ and V_oc = 10 V. With 6 kΩ: V_out ≈ 10 * (6000/8000) = 7.5 V. With 5 kΩ: V_out ≈ 10 * (5000/7000) ≈ 7.14 V. The 6 kΩ case has less sag, matching the rule of thumb to use a load at least 10× the source resistance.


Why Other Options Are Wrong:

  • Incorrect: Contradicts the divider formula; larger R_L reduces loading.
  • Only true for AC sources: The reasoning is resistive and applies to DC as well.
  • Only true when source resistance is zero: If R_th were zero, both loads would see the same ideal source voltage; the statement remains consistent with the general rule for R_th > 0.


Common Pitfalls:
Ignoring the source/ divider's Thevenin resistance, or assuming that higher-ohm loads always draw "more" voltage drop in the source. In reality, higher-ohm loads draw less current and thus cause less droop.


Final Answer:
Correct — a 6 kΩ load produces a smaller output decrease than a 5 kΩ load on the same divider.

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