Final answer:
Sparks can be thrown up to 2.5 cm with a voltage of about 75 kV or up to 5 cm with 150 kV. The limit on sparking voltage affects conductors, power transmission lines, and surfaces with points versus smooth surfaces. Humid air can break down at a lower field strength, allowing sparks to jump through it more easily.
Step-by-step explanation:
Sparks can be thrown up to 2.5 cm with a voltage of about 75 kV, or up to 5 cm with 150 kV. This limit restricts the voltages that can exist between conductors, such as on power transmission lines.
A smaller voltage can cause a spark if there are points on the surface, as points create stronger electric fields than smooth surfaces.
Additionally, humid air breaks down at a lower field strength, allowing sparks to jump through it with smaller voltages. The largest voltages, like those from static electricity, can build up on dry days.