A. A mask containing a hole in the shape of the letter L is placed between a screen and a trio of very small bulbs as shown at the right.   On the diagram of the screen, sketch what you would see on the screen when the bulbs are turned on.

B. Which of the following things would happen to the pattern of light on the screen if the actions described in B1-B2 were carried out? After each action, the original situation is restored. (The changes do not cumulate.)

B1. The mask is moved a bit to the left.

B2. The bulbs are moved upward a bit