what would one have to do if one wanted to use the galvanome

Solution

For the sake of this explanation, let us assume a very sensitive galvanometer with 100 Ohm coil resistance, and 100 microAmperes current for full-scale deflection. Thus, by Ohms Law, the full-scale deflection will require 10 mV across the terminals.

For a voltmeter. If we needed a full-scale reading of 50 Volts, we would need to ensure that 50 Volts would cause 100 microamperes (assumption) to flow through the galvanometer.

Ohms Law tells us that a resistor of 500 kOhms would pass 100 microAmperes through it, if exposed to 50 Volts. If we were to put our galvanometer in series with this current path, we\'d have an excellent 50-Volt Voltmeter. In this case, again, the 100 Ohm coil resistance is negligible in comparison to the 500 kOhm resistor, so we can ignore it.