Consider the circuits shown in Fig. 1 and Fig. 2. Assume that you have the meter

Question

Consider the circuits shown in Fig. 1 and Fig. 2. Assume that you have the meter readings, that they are free of error, and that you have the characteristics of each meter. I. Derive a formula for calculating the true value of Rx for the circuit 1FIGI FIG.2 of Fig. 1. 2. Do the same for Fig. 2 An attempt to eliminate the above errors can be made as follows: Use the circuit of Fig. 1 to measure the voltage. Then disconnect the voltmeter and measure the current. Although this might seem to avoid the error pointed out above, it should be noted that when the voltmeter is disconnected, less current flows, hence there is less voltage drop across the ammeter, and hence there is more voltage drop across the resistor. Therefore, the current measured corresponds to a larger voltage across the measured. A similar attempt may be tried with Fig. 2, shorting out the IL INTHELABORATOoe colors of their stripes and the corresponding nominal values. Read the equipment notes on resistors A. Select resistors from the instructor at the froat table as follows. Record t resistor than that I. Nominal value-47 ohms ± 5%. 2. Nominal value = 150 ohms ± 5%. 3. Nominal value 2000 ohms ± 5%. while reading the voltage. Here, too, the voltage and current readings to the same circuit conditions and there

Explanation / Answer

Let us suppose that the meter readings of Ammeter is I & of Voltmeter is V. Also suppose that the internal resistance of Voltmeter is Rv.

Applying KCL to fig 1 we get

I = V/ Rx + V/Rv

The total resistance of fig 1 can be calculated as

1/R = 1/Rx + 1/Rv

R = Rx Rv / Rx + Rv

Now applying KVL in fig we get

2 = I (Rx Rv)/ (Rx + Rv)

or 2Rx + 2Rv = I Rx Rv

or Rx = 2Rv/ (I Rv-2)

Now consider figure 2

Equivalent resistance of the circuit shall be R = Rx Rv / Rx + Rv

Now applying KCL for this circuit we get

10/R = I + V/Rv

putting the value of R we get

(10Rx + 10 Rv)/ Rx Rv = I + V/Rv

or 10Rx + 10Rv = IRv Rx + VRx

or 10Rv = (IRv + V - 10) Rx

or Rx = 10Rv/ (IRv + V - 10)

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