QUESTION: In part 2, why were the voltmeters exchanged and a second set of readi

Question

QUESTION: In part 2, why were the voltmeters exchanged and a second set of readings taken?

Voltmeter across unknown resistance: Connect the circuit shown in Fig. 1, using resistor #1. Have the instructor check your connections, and after receiving his approval, close the switch and read the voltmeter and ammeter simultaneously. Voltmeter across unknown resistance and ammeter: Connect the circuit shown in Fig. 2, using resistor #1. After the instructor has approved your connections, close the switch and read the ammeter and voltmeter. Comparison method of measurement of resistance: With the known resistance R_S (resistance box) set at about twice the value obtained for resistor #1 as found in 1 above, connect it and resistance #1 in series. Connect one voltmeter across each resistor, as in Fig. 3. After the instructor has given his approval, close the switch. Record the voltmeter readings, and open the circuit. Exchange voltmeters, close the circuit, and again record the voltmeter readings. Use the first two readings in the relationship R_X/R_S = V_X/V_S; then use the second two readings similarly. Take the average of the two values for R_X as the most probably correct value.

Explanation / Answer

while taking the measurements in fig 1 connection, voltameter will give measurements of voltage across R and Ammeter so value of R will be higher than that of actual. And similarlly while taking measurements in Fig 2 connection, The a meter will measure total curent( Through R and Voltmeter) so value of R calculated from this will be lower than that of actual. So Both measurements are taken and its average is considered as the final value of R.

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