Question

what word(s) in box a would best complete the model below? b changes electric field box a changes electrons powers magnetic field coils

Explanation:

According to Maxwell's equations, a changing electric field generates a magnetic field, and a changing magnetic field generates an electric field. This is the basis of electromagnetic waves. Among the options, "Magnetic Field" fits this relationship as it is the entity that is generated by a changing electric field (and vice - versa in the cycle). Electrons are particles, powers is a rather vague term in this context, and coils are physical objects used to manipulate fields but not the field itself in this fundamental relationship.

Answer:

Magnetic Field