Ca (valency 2) and O ((valency 2)

stands for electromotive force and it is measured in volts. despite its name, it is not actually the force in the sense of being a "pushing" or "pulling" (not measured in newtons).an equation that relates emf,  ℰ,  to a battery's terminal voltage, v, current, i, and internal resistance, r, is    ℰ = v + irin this case, the emf can be interpreted as a voltage—a difference in electric potential.i would not say that it would be considered an energy. if emf can be defined as the energy/work per a unit charge from a battery or other electric source, then it is not strictly energy.

Amagnetic field "does not" interact with stationary electric charges. so, a.hope my answer you : )

Answerapplying a direct current to a non magnetic material in order to create a electromagnetic field; plz check first good luck;

Lexy is correct because angle r is between the incident wave,  n  = 0, and a diffracted wave.