Final answer:
Two planes intersect in exactly one line, which is a concept utilized in physics, particularly in electrostatics for creating uniform fields and in circuit analysis where currents at junctions are considered.
Step-by-step explanation:
Planes ADHE and EFGH intersect at only one line due to the geometric principle that two planes intersect in exactly one line. This concept is significant in physics when studying systems that can be approximated as two infinite planes, such as creating uniform electric fields. Using the principle of superposition, the electric field from two intersecting planes can be determined based on the field resulting from a single infinite plane.
The concept is also relevant in electricity and circuits, as represented by the mention of the junction rule and loop rule in circuit analysis, where currents entering and leaving a junction must be equal, necessitating multiple equations to solve for unknown values. Additionally, understanding the intersection of planes is fundamental in mechanics problems, like determining the velocity of an object in different reference frames, such as a plane's velocity concerning the ground when compounded with air motion.