The GATE Grind

GATE 2025 IN – Question 21

Measurements · Voltage current and power measurement · 1 mark · Multiple choice

In a single-phase AC circuit, a wattmeter measures power consumed by load resistance $R_L$ under excitation $V_S$. The same meter is connected in Topology A and Topology B as shown, with branch currents and voltage drops marked. Which condition ensures low reading error in both topologies?

Diagram for GATE 2025 IN question 21
  1. $V_L\gg V_C$ for A and $I_L\gg I_P$ for B
  2. $V_L\gg V_C$ for A and $I_L\ll I_P$ for B
  3. $V_L\ll V_C$ for A and $I_L\ll I_P$ for B
  4. $V_L\ll V_C$ for A and $I_L\gg I_P$ for B

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Correct answer: (A) $V_L\gg V_C$ for A and $I_L\gg I_P$ for B

Explanation

Topology A includes the current-coil voltage drop in the sensed voltage, so load voltage must greatly exceed that drop: VL≫VC.

Topology B includes pressure-coil current in the measured current, so IL≫IP.

Together these are **A**.