Select the reasons why most professional telescopes are reflectors rather than refractors. A mirror can collect light more efficiently than a lens. Only the front surface of a mirror has to have a precise shape. Lenses are not subject to chromatic aberration. A lens has to be supported only around its edges. Reflecting telescopes have shorter focal lengths than refracting telescopes. It is easier to make a large reflecting telescope than a large refracting telescope.

Four objects each with charge +2.0×10−7c are located at the corners of a square whose sides are 2.0 m long. part a what quantities can be determined using this information? check all that apply. the electric force on a charged object placed at the center of the square. the mass of each object. the total electric potential energy of the system consisting of the four charged objects. part b find the electric force on a charged object placed at the center of the square.