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The ratio of the readings of two wattmeter connected to measure power in a balanced three phase system is 5 : 3 and the load is inductive. The power factor of the load is
1. 0.92 lagging
2. 0.92 leading
3. 0.6 lagging
4. 0.6 leading

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Correct Answer - Option 1 : 0.92 lagging

In two wattmeter method,

\(\begin{array}{l} \tan \phi = \frac{{\sqrt 3 \left( {{W_1} - {W_2}} \right)}}{{{W_1} + {W_2}}}\\ \Rightarrow \tan \phi = \frac{{\sqrt 3 \left( {\frac{{{W_1}}}{{{W_2}}} - 1} \right)}}{{\left( {\frac{{{W_1}}}{{{W_2}}} + 1} \right)}}\\ \Rightarrow \tan \phi = \frac{{\sqrt 3 \left( {\frac{5}{3} - 1} \right)}}{{\left( {\frac{5}{3} + 1} \right)}} = \frac{{\sqrt 3 }}{4}\\ \Rightarrow \phi = 23.41^\circ \end{array}\)

Power factor, \(\cos \phi = 0.917\)

Given that the load is inductive and hence power factor is lagging.

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