Question

The voltage and current drawn by a resistive load are measured with a 300 V voltmeter of accuracy ± 1% of full scale and a 5 A ammeter of accuracy ± 0.5% of full scale. The readings obtained are 200 V and 2.5 A. The limiting error (in %) in computing the load resistance is (up to two decimal places) ____.

Answer 1

Voltmeter – 300 V ± 1% FSD

Ammeter – 5A ± 0.5% FSD

Voltmeter – 300 V ± 3 V

Reading = 200 V

% limiting error \(= \frac{3}{{200}} \times 100 = 1.5\%\)

Ammeter – 5A ± 0.025A

Reading = 2.5 A

% limiting error \(= \frac{{0.025}}{{2.5}} \times 100 = 1\%\)

\({R_L} = \frac{V}{I}\)

% limiting error in R = % limiting error in V + % limiting error in A

= 1.5 + 1 = 2.5 %