Final answer:
Replacing a 1.5 V battery with a 3 V battery in a circuit will increase the current if resistance remains the same. In a parallel circuit, the voltage across each resistor remains the same as the voltage across the battery; if resistors have 2 V, then the battery also has a voltage of 2 V.
Step-by-step explanation:
When a 1.5 V battery is removed from a circuit and replaced by a 3 V battery, the voltage across the entire circuit increases. This increase in voltage will result in a higher current, assuming the circuit's resistance remains unchanged, according to Ohm's law (V = IR, where V is voltage, I is current, and R is resistance). If the circuit components are designed to handle the increased current without overheating or being damaged, the circuit should function with more electrical energy being provided to its components.
When dealing with a parallel circuit, however, replacing a battery does not change the voltage across the resistors that were already receiving the higher voltage. In a parallel circuit, all components share the same voltage, so in the condition where the resistors each have a voltage of 2 V, the voltage across the battery must equal to the voltage across any of the resistors, which would also be 2 V.