Question

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Voltmeter Vo 0 Figure 3.3: Circuit used to observe the effect of test equipment on a measurement. Internal resistance problem. Suppose that in Figure 3.3, Vo-13V, Ri 250kS2, R2 -375k2, and R1.3MS2. Initially, the voltmeter is disconnected. EXAMPLES: What is the voltage across R2? [Answer: 7.8 V] What is the voltage across R2 with the meter connected? [Answer: 6.99310344827586 V.] QUESTION: If the internal resistance of the meter were 13 M Ω, what is the voltage across R2? Volts

Answer 1

if v_0 = 13v, R_1 = 250 k ohm, R_2 = 375 k ohm, R_i = 1.3 M ohm but initially voltmeter is disconnected means the resistance of voltage meter, we have to ignored so, example, we have to find voltage across R_2, by voltage division series method, V_R_2 = voltage across R_2 = R_2/R_1 + R_2 middot V_0 = (375 k oh/375 k ohm + 250 k) middot 13 v = 375 k ohm/625 k ohm times 13 v = 0.6 times 13 v \r\n we have to find voltage across R_2 with meter is connected means out figure is as given in figure, so from fir, R_i & R_2 are parallel so, by resistance is parallel then, R_equivalent = R_e = R_i times R_2/R_2 + R_i = 1.3 M ohm times 375 k ohm/(1.3 M ohm + 375 k ohm) = 1.3 times 10^6 ohm times 375 times 10^3 ohm/(1.3 times 10^6 ohm + 375 times 10^3 ohm)