Ysolde tries on sunglasses at a store rack. She holds a second pair in front of the first and looks through both lenses at once.
Both lenses are tinted the same gray. So stacking them should just make the view a little darker. Ysolde turns the second pair slowly, and something stranger happens.
These lenses are polarizing filters. A polarizing filter looks like plain tinted glass, but it treats light in a special way this topic will uncover.
Hold two polarizing filters together, lined up the same way, and the view through the pair is at its brightest.
Now turn the second filter while the first stays still. The view grows dimmer, a little at a time.
At a quarter turn (90°), the view reaches darkness: the patch where the filters overlap is nearly black.
The pattern is steady the whole way. Between lined up and a quarter turn, the view is dimmer than lined up but not yet black.
Plain tinted lenses never do this. Turning one tinted lens on another changes nothing. Whatever these filters are doing to the light, the next lesson builds the model that explains it.
Zeno lines up two polarizing filter squares from the class kit and the patch between them is bright. He turns the second square a quarter turn. What does he see?
Lined up gives the brightest view.
A quarter turn is the other end of the pattern: the overlap patch dims steadily on the way and reaches darkness there.
The overlap patch is nearly black at the quarter turn.
Amity looks through two stacked camera filters. The view is dimmer than when they were lined up, but she can still see the scene clearly. Roughly how far has the second filter been turned?
Dimmer than lined up rules out the lined-up setting.
Still clearly visible rules out the quarter turn, where the view is nearly black.
Between those two settings the view is dimmer but not yet dark.
The second filter sits somewhere between lined up and a quarter turn.
Bard stacks two polarizing filter squares with their settings lined up. How does the view through the pair compare with the other settings?
Amity turns the second of two stacked polarizing filters until it sits a quarter turn from the first. What does she see through the overlap?
Zeno says: 'Between lined up and a quarter turn, the view through two stacked polarizing filters is dimmer than at lined up, but not yet black.' Is Zeno correct?
Two polarizing filter squares sit lined up in a clamp. Ysolde turns the second square an eighth of a turn (45°). Compared with lined up, how does the view through the overlap change?
Bard turns the second of two stacked polarizing filters slowly and steadily from lined up to a quarter turn. Which statement describes the brightness of the view during the turn?
Amity looks through two stacked polarizing filters and the overlap patch is nearly black. How is the second filter set, relative to the first?