Final answer:
Power lines are more efficient when power is transmitted at higher voltage and lower current to minimize power loss, hence the answer is A) Voltage, Current. High voltage enables lower current for the same power, reducing power loss due to the fixed resistance in the transmission lines.
Step-by-step explanation:
Power lines lose less energy if power is transmitted at higher voltage and lower current. The correct answer to the student's question is A) Voltage, Current. This is because power loss in transmission lines is a function of the current squared times the resistance (Ploss = I2R), and a higher voltage allows for a lower current to transmit the same amount of power, hence reducing the power loss. In practice, transmission lines are operated at high voltages, often hundreds of kilovolts, to minimize these losses. Lower voltages would require higher currents, which would increase power loss in the lines due to their fixed resistance. It's also worth noting that alternating current (AC) voltage is typically used in large-scale power distribution systems because it is easier to raise and lower AC voltage levels with the use of transformers. As a result, power companies significantly reduce ohmic losses by raising the voltage level for long-distance transmission and then lowering it for residential distribution.