Although an ideal voltmeter has an infinite internal resistance, this theoretica

Question

Although an ideal voltmeter has an infinite internal resistance, this theoretical ideal is usually not met in practice. The voltmeter in the Figure has an internal resistance of 3 x 109 ? and is used to measure the voltage across the resistor R2 as shown. Attaching this non-ideal voltmeter decreases the voltage across R2. Calculate the magnitude of this decrease using an emf of 9 V and R1 = R2 = 200 k?.

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Explanation / Answer

most importanlty figure is missing

iam assumin R1 and R2 are is sereis

so now resistance across R1 and R2 = R1+R2 = 350+350 = 700 k ohms

when voltmeter is connected only across R2,

they both will be in parallel Combintion

so

Rnet = R' = 350000 * 6e9/(3.5e5 +6e9)

R' = 350 k ohms

so currrent i = V/R = 16/350000 = 4.57 e-5 Amps

PD across R2 = iR = 4.57 e-5 * 350000

V2 = 16 Volts

------------------------------

Rnet = R' = 70000 * 6e9/(7e6 +6e9)

R' = 700 k ohms

so currrent i = V/R = 16/70000 = 2.28 e-5 Amps

PD across R2 = iR = 2.28 e-5 * 350000

V2 = 7.98 Volts

so PD = 16-8 = = 8 Volts ---<<Answer

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