# Answer to Question #97559 in Electrical Engineering for Ojugbele Daniel

Question #97559
A voltmeter having a sensitivity of 1200Q/V and read 100V on it's 220V scale when connected across an unknown resistor in series with a milliameter when the millimeter read 5mA calculate
(i) the apparent resistance of the unknown resistor.
(ii) the actual resistance of the unknown resistor.
1
2019-11-04T06:31:13-0500

What we have here: a voltmeter with sensitivity 1200 ohm/volt, with scale with maximum 220 V, which shows 100 V. We know that the real current is 5 mA. How are all they connected? Assume like this: Calculate the resistance of the voltmeter on its 220 V range:

"R_V=1200\\cdot220=264000\\space\\Omega."

(i) The apparent resistance (with an assumption that the voltmeter's resistance is infinity):

"R_A=\\frac{100}{0.005}=20000\\space\\Omega."

(ii) Find the actual resistance. 5 mA is the common current:

"0.005=\\frac{V(R_V+R_x)}{R_VR_x}=\\frac{V(264000+R_x)}{264000R_x},\\\\\n\\space\\\\\nR_x=21639.3\\space\\Omega."

(iii) The error is:

"\\Delta=\\frac{|20000-21639.3|}{21639.3}\\cdot100\\%=7.6\\%."

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