Reflecting telescopes are popular because they're
a. more powerful than a refracting telescope.
b. smaller than a refracting telescope.
c. easier to build than a refracting telescope.
d. more durable than a refracting telescope.

C. easier to build than a refracting telescope

Big mirrors used in reflecting telescopes are easier and cheaper to make than big lenses which would cost more because of the quality of glass required to make refracting telescopes

Lx bxh

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.