An outdoor apparel company is testing two configurations for a new heated vest. The vest uses two identical resistive heating elements, each of resistance RRR, connected to a rechargeable 12 V battery pack. The engineers set up two test designs, Design A and Design B, as shown in the schematic diagrams below:
State which design will deliver the highest rate of thermal energy (heating power) to the vest and explain why in terms of equivalent electrical resistance, potential difference (voltage), and current. In your answer, identify the critical control variables the engineers must keep constant to ensure a scientifically valid comparison.