Meters: A galvanometer has an internal resistance of 100 Ω and deflects full-scale at a current of 2.00 mA. What size resistor should be added to it to convert it to a millivoltmeter capable of reading up to 400 mV, and how should this resistor be connected to the galvanometer?
A) 50.0 Ω in series with the galvanometer
B) 50.0 Ω in parallel with the galvanometer
C) 75.0 Ω in parallel with the galvanometer
D) 100 Ω in series with the galvanometer
E) 100 Ω in parallel with the galvanometer

Question

Quizplus · Accepted Answer

To convert a galvanometer to a millivoltmeter with a full-scale deflection at 400 mV, the total resistance needed for the circuit can be calculated using Ohm's law (V = IR), where V is the voltage (400 mV or 0.4 V), and I is the current (2.00 mA or 0.002 A). The total resistance required is V/I = 0.4 V / 0.002 A = 200 Ω. Since the galvanometer already has an internal resistance of 100 Ω, an additional 100 Ω resistor is needed in series to achieve the total resistance of 200 Ω.

Meters: a Galvanometer Has an Internal Resistance of 100 Ω