In the figure below, a voltmeter of resistance RV = 1000 Ohm, and an ammeter of

Question

In the figure below, a voltmeter of resistance RV = 1000 Ohm, and an ammeter of resistance RA = 3.00 are being used to measure a resistance R in a circuit that also contains a resistance R0 = 100 and an ideal battery of emf = 15.0 V. Resistance R is given by R = V/i, where V is the voltmeter reading and i is the current in resistance R. However, the ammeter reading is not i, but rather i', which is i plus the current through the voltmeter. Thus, the ratio of the two meter readings is not R, but only an apparent resistance R' = V/i'. If R = 80.0 Ohm: What is the ammeter reading? A What is the voltmeter reading? V What is R'? Ohm If RV is increased, does the difference between R' and R: increase decrease stay the same

Explanation / Answer

a) first combine voltmeter and R

1/R = 1/1000 + 1/80

R= 1000*80/1080= 74.07 ohms

then combine with ammeter and Ro

Req = 74.07 + 100 + 3 = 177.07

so I = 15/177.07= 0.0847 A

b) V = 74.07*0.0847= 6.27

c) R' = 6.27/0.0847= 74.03 ohms

d) less curent through voltmeter so difference will decrease

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