Question

The voltmeter reads 117 V and ammeter reads 0.13 A .If the resistance of ammeter and voltmeter are 9 kilo ohm and 0.015 ohm respectively ,find the value of R. 3marks

Answer 1

R = 899.985Ω.

The ammeter gives a lecture of I = 0.13A through the resistor and the voltmeter gives a lecture of V = 117V between the points a and c, the ammeter resistance is Ra = 0.015Ω. So, the voltmeter reading is the sum of the potential difference Vbc (through the ammeter) and Vab (through the resistor).

To obtain the voltage Vbc through the ammeter from its known current and resistance, Ohm's law is used.

Vbc = I*Ra = (0.13A)(0.015Ω) = 0.00195V

Vab = V - Vbc = 117V - 0.00195V = 116.99805V

We know that Vab = I*R. Clear R from the equation:

R = Vab/I = 116.99805V/0.13A = 899.985Ω