Question

Part II. Conversion of a Galvanometer into a Voltmeter a) Let's now switch to the circuit in Figure 2. Set it up and have it checked by your instructor before closing it. For Rause the theostat (from the greck p owitam resistance of 2000 Calculate the resistance Raneeded to make your 0-1.0 mA galvanometer work as a Qur voltmeter (neglect Ro) and insert it in the circuit 3U RM" .3k-2 b) Use your voltmeter to measure the voltage of 1 and 2 batteries in series vi- 145mA x 36 22 1.35V V₂- 185mA x3k2 = 2.550 Measure V, and V, using a multimeter V."- 1.293 V2"-2.6 Compare the two couples of measurements: Vi-V," 1.35U-1.293-0.057V V2-V₂"- 2.55-2.60=0.05V Are your measurements in accord with the theory? Explain. Reducing the resistance RAB changes the measured voltages? Explain. Part III. Internal resistance

Answer 1

a)

The differences in the voltages of batteries 1 and 2 measured using the voltmeter converted from galvanometer and multimeter are very small and hence the conversion is successful.

b)

Galvanometers are actually used to measure the current in electrical circuits. So when we need to convert galvanometer to voltmeters of different ranges, the maximum measurable current remains the same. It is the series resistance $R_{M} = \frac{V}{I}$ decides the voltage range that can be measured using the voltmeter. Thus reducing resistance also reduces the maximum measurable voltage.