Final answer:
To calculate transmission efficiency, it is necessary to know the power at the receiving end for an AC system and to compare power transmitted to input power in a DC system. High voltages are more economical for power transmission, especially when using AC for large-scale distribution.
Step-by-step explanation:
Transmission efficiency is important to understand in the context of high-voltage and low-current choices for power transmission, as this minimizes the ohmic losses in the lines. The examples provided illustrate situations involving power transmission: single-phase alternating current (AC) where certain parameters such as voltage, current, and phase angles are specified; and direct current (DC) where sending voltage and line resistance are given along with power transmitted. To calculate the transmission efficiency for AC, one would need to account for the voltage drop, phase angle difference, and current to find the power at the receiving end and compare it to the power at the sending end. For DC, efficiency calculations would involve the using power transmitted and comparing it to the power input considering the line resistance. Unfortunately, without calculating the receiving power in situation (i) and without the power dissipated over the resistance for situation (ii), we cannot provide a complete solution. High voltages are more economical for transmitting power, and AC voltage is much easier to raise and lower, so that AC is used in most large-scale power distribution systems.