L

Below is a particular arrangement of a point source, a rectangular-shaped blocker and a screen. The shadow region is shown on the front view of the screen. Imagine that the blocker were moved to the right, closer to the screen. Assume the positions of the light source and screen remained unchanged. What would happen to the shadow region on the screen? A. It would become smaller. B. It would remain the same size. C. It would become larger.

(A) It would become smaller. As you move the square blocker closer to the screen, the image on the screen gradually decreases until it reaches the size of the blocker when the blocker touches the screen. See the light ray diagram below.

Below is a setup of an extended source a certain distance from a pinhole. The screen is the same distance on the other side of the pinhole. The screen shows a sharp upside down image of the source. Now imagine that the distance between the source and pinhole is doubled and the distance between the screen and pinhole is halved (one-half as much). If that were done, what would happen to the size of the image on the screen? A. It would be about the same size. B. It would be much larger. C. It would be much smaller.

(C) It would be much smaller. Moving the source further away from and moving the screen closer to the pinhole both have the effect of makng the image smaller. See the light ray diagram and screen view below.

Y gel =

-B

M gel =

-G

R gel =

-G, -B

C gel =

-R

G gel =

-R, -B

B gel =

-R, -G

B + G

C (Cyan)

The light ray diagram below is supposed to show a person looking at a white book that he is holding in his hand. There is a black-colored barrier blocking light from the lamp from directly going to the book. The ceiling is a large mirrored surface. A. The light striking the ceiling should reflect in more than one direction, rather than in the one direction as shown. B. The light striking the book should only reflect in one direction, rather than in the many directions as shown. C. Light reflecting from the book should also be shown entering the eye. D. A and B only are wrong. E. A and C only are wrong. F. B and C only are wrong. G. A, B and C are all wrong.

Choice C is the best answer.

R+ B

M (Magenta)

Two point sources of light, labeled 1 and 2 in the picture below are placed in front of a flat mirror. Source 2 is closer to the mirror and source 1 is further away. A person, represented here by an eye, is looking at the images of the two sources in the mirror. Which image, if either, is closer to her eye? A. The image of source 1 is closer to her eye. B. The image of source 2 is closer to her eye. C. The images of both sources are the same distance to her eye.

The correct answer is choice B. The image of the source closest to the mirror, source 2, appears to be closer to the viewer, even though that source is further from the viewer than source 1. The image below provides a snapshot of this scenario, complete with light rays and their "backward extensions".

R + G + B

W (White)

Color Spectrum

We usually identify several different colors in the visible spectrum. A common set is Red (R), Orange (O), Yellow (Y), Green (G), Blue (B), and Violet (V). However, when discussing color vision, for convenience, we divide the complete spectrum into three broad bands, Red (R), Green (G), and Blue (B).

R + G

Y (Yellow)