Which idea did Ptolemy’s model use to explain why the planets appeared to move backward as they moved in their orbits? The planets spun in epicycles.
The planets rotated on their axes.
The planets revolved around the Sun.
The planets were made of different materials.

Light from two different sources are incident upon the same side of a polarizing filter. light from one source is polarized with total intensity ip, while light from the other source is unpolarized with total intensity iu. as you rotate the polarizing filter through 360 degrees, the intensity of the transmitted light on the other side varies by a factor of 9. what is the relative intensity of the initial polarized source to the unpolarized source, or ip/iu?