A student who doesn\'t really know what he is doing is accustomed to making meas

Question

A student who doesn't really know what he is doing is accustomed to making measurements with very good (nearly IDEAL) meters. However, the student is currently using meters that are not so good. He uses the two meters to measure the resistance of R_1 by taking R_1 = where deltaV is the voltmeter reading and I is the ammeter reading. When you do not know the resistances of the meters, this is a really bad idea but the student does not realize this. The student is not sure whether to connect the voltmeter to the left or right of the ammeter (dashed lines in the figure). a: If the connection is made to the right of the ammeter, will the resulting resistance measurement be too high or too low? Explain. b: If the connection is made to the left of the ammeter, will the resulting resistance measurement be too high or too low? Explain. c: Determine the measurement which would result from the two different connections. Use epsilon = 50 V, R_internal = 25ohm R_voltmeter = 4200ohm R_ammeter = 15ohm and R_1 = 600ohm.

Explanation / Answer

a) It wont be too high or low because Ammeter generally has a low resistance which won't make much difference to overall resistance but will give correct reading.

b)  Again it wont be too high or low because Ammeter generally has a low resistance which won't make much difference to overall resistance but will give incorrect reading ( a bit lesser)

c) Let Rv RA and RI be Resistance of voltmeter ammeter and internal respectively

When connected on right

R1 and Rv will be in parallel connection

Solving

600*4200/(600+4200)=525ohm

Now this resistance will be in series with RA and RI

Rnet = 525+15+15=555ohm

When connected on left

RA and R1 will be in series= 15+600=615ohm

Now this resistance will be be in parallel to RV = 615*4200/(615+4200) =536.45ohm

Now this will be in series with RI = 536.45+15=551.45 ohm

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