The instantaneous voltages at three terminals marked X ,   Y and Z are given by V X = V 0 sin ⁡…

The instantaneous voltages at three terminals marked X, Y and Z are given by
VX=V0sinωt
VY=V0sinωt+2π3  and
VZ=V0sinωt+4π3.
An ideal voltmeter is configured to read rms value of the potential difference between its terminals. It is connected between points X and Y and then between Y and Z . The reading(s) of the voltmeter will be
  1. VXYrms=V0
  2. VYZrms=V012
  3. Independent of the choice of the terminals
  4. VXYrms=V032

Solution

Potential difference between X and Y=VX-VY

Potential difference between Y and Z=VY-VZ

Phasor of the voltages:

From phasor diagram the peak value of Vx-Vy can be calculated from parallelogram law

Vx-Vypeak=VX2+VY2+2VXVYcos60                   =V02+V02+2V0V0×12                   =3V0

    VX-VYpeak= 3V0

Vx-Vyrms=VXYrms=3V02

Similarly  Vy-Vzrms=VXYrms=3V02

^

Asked in: JEE Advanced 2017 (Paper 2)

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