Final answer:
The voltmeter in the circuit will measure a voltage of 20 volts, because it is placed in parallel with the battery, and the internal resistance is negligible.
Step-by-step explanation:
The voltage measured by the voltmeter in the circuit described is equal to the terminal voltage of the battery, as the voltmeter is placed in parallel with the battery or either of the resistors and the internal resistance is negligible. When resistors are connected in series, the total resistance in the circuit is the sum of individual resistances. Since each resistor is 20 ohms and there are two resistors, the total resistance is 40 ohms. According to Ohm's law, which states that V = IR (where V is voltage, I is current, and R is resistance), you can calculate the current in the circuit using the formula: I = V/R. Considering the battery is 20 volts, the current (I) equals 20 V / 40 Ω = 0.5 A. However, since a voltmeter in parallel measures just the voltage across it, the voltage reading would directly be the voltage of the battery which is 20 volts. Therefore, the correct answer is B. 20 V.