Question

RI Al huugh dn ideal vullme er has an 'nlinite in erna resis anue his lheur etical icledl is usually no me in practice The vollrreler in the Figure has an "ternal tesis an e o 6 x 10。Ω dnd is Attaching this non-ideal voltmeter decreascs the voltage across R2. Calculate the magnitude of this decrease using an emf of 20 used to measure the voltage across the resistor R as shown. Vand R1 = R2 = 150 kS2. R2 n V Subril Aiswer Iries 1/10 Prevlous Trles

Answer 1

Resistance of voltmeter = 6*10⁹ Ohm

Resistance of R2 = 150000Ohm

Equivalent reistance of voltmeter and R2 = (6*10⁹*150000)/(6*10⁹+150000) = 149.996 kOhms

This in series with R1=150000 Ohms

Equivalent resistance of circuit = 149.996+150=299.996 k Ohms

Battery emf = 20 V

Total current in circuit = 20/299996=6.66675*10^-5 ampere

Potential drop across R2 = [20-(6.66675*10^-5*150000)]=9.999875 V

If voltmeter had infinite resistance,then potential drop across R2 would have been =10 V

Therefore, magnitude of decrease in voltmeter reading = 10-9.999875=1.25*10^-4 V