NCTI Service Technician Practice Exam

When both current and resistance in a transmission line increase, heat loss within the line increases significantly due to the relationship described by Joule's law, which states that the power loss as heat (also called I²R losses) is proportional to the square of the current multiplied by the resistance. Specifically, the formula for power loss is P = I²R, where P represents power loss, I is the current, and R is the resistance.

As current increases, even a small increase in the current can lead to a substantial rise in heat loss because it is taken to the power of two. Simultaneously, if resistance increases, it further compounds this effect. Therefore, both factors working together cause heat loss to increase significantly, making it a critical consideration in the design and operation of transmission lines.

The other options do not accurately reflect the relationship between current, resistance, and heat loss in transmission lines, as both decreasing and holding constant would not take into account the direct effects of increased current and resistance on heat generation. Additionally, voltage variations alone do not dictate heat loss without considering current and resistance directly.