image object Figure 2: An object placed a distance d, from a positive-f lens forms an image at a distance d; from the lens.Explanation: Look at Fig. 2 to help you finish the following argument explaining your observation of what happens to the image when half the lens is blocked. We know that mays go out in all directions from each point on the object. To be specific, we now consider only those rays leaving from the tip of the arrow. Most of those rays do not hit the lens; they continue in straight lines and if your eye intercepts them, you say "I see the tip of the arrow." Thus, the entire face of the lens is covered with rays from that one point. When these rays go through the lens they refract and they all head for ... [Here's where you fill in this part of the argument with a short phrase. The argument will continue below. Uniquely specify where these rays go. Don't just fill in the image.] Nothing in the argument above depends on whether the ray from the tip goes through the top or bottom half of the lens. However, if we now consider rays originating from a point on the base of the arrow, one thing does change. We know rays from this one point also fill the entire face of the lens, but after passing through the lens, rays from this point all head for... [Again, fill in a short phrase.] Now synthesize the argument and the observation. Thus, my observation of what happens when half the lens is blocked is consistent with the arguments above. When half the lens is blocked ... [Here, you should finish this sentence and perhaps add one or two more sentences that explain any change in the appearance of the image.]6. Leave the lens and object fixed with the reduced image sharply focused on the screen. Now slowly move the screen forward or backward. How far must you move it before the image is totally blurry? Explain why the image gets blurry. Be specific. Don't just say because the screen is not at the correct image distance. Hint: the explanation is an extension of the reasoning above and it will again help to start the reasoning process by considering only rays leaving the tip of the object. Just keep in mind that the rays travel in straight lines after leaving the lens and continue in straight lines both before and after they converge to the corresponding image point. Think about a "cone" of light rays from the source point to the lens and from the lens to the image point. Put the screen back at the focused position. Put the lens aperture (paper with a 3 cm hole) over the lens. As when you covered half the lens, the image will become dimmer because fewer rays are involved in making the image. If you now move the screen forward or backward, the image will still get blurry. Predict whether you will have to move the screen more, less, or the same as before to reach the same level of blurriness. Explain the logic of your prediction. Now try it and describe the results. How far (in cm) must you move it before the image is totally blurry? If necessary, correct your explanation. Using an aperture in front of a lens helps increase the depth of focus in a picture. With a larger area lens, objects in front or behind the subject in focus will be out of focus. Aperturing down the lens will allow these other objects to stay more in focus with the subject.7. Remove the lens aperture and put the screen back at the focused position producing the reduced image. Remove the paper screen from its cardboard mount without moving the mount so the image is now on the cardboard mount. Mark the mount at the middle of the image and cut a centered 3 cm circular hole in the mount as shown in Fig. 7. Again, remember to always push the knife away from your hands and body when cutting the hole. Replace the paper so the hole is covered and again make the reduced image appear on the screen. Now remove the paper screen-again without moving the mount so the image is now in the hole in the cardboard and thus not viewable. Is it really not viewable? Do you think there is anyplace you can position your eye so that you will be able to see the image that was previously on the screen? Why or why not? Now try it. Stand behind the screen and look through the hole in the screen mount toward the lens and object. Don't put your eye up too close to the hole. Stay at least 50 cm behind it. Try to locate the image by moving your head left and right and up and down. "Touch" the image by poking your finger through the hole. Where is the image located? When you move your eyes up and down, left and right, where are they when the image is no longer viewable. That is, describe where you have to position your eye to see the image and explain why this positioning is necessary.\f