Lab & Pre-lab #11

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Lenses and Images v 0.1 Step 2: Remove the screen. Now look toward the lens from a position about two feet beyond where the screen had been located. Look for the image of the ”F” floating in front of the lens. It will be inverted, just like the image that had been projected on the screen. It should appear to be in the same position where the screen had been. Each member of your group should make this observation. lamp former screen position eye Figure 8: Locating a real image with your eye, using parallax Step 3: To locate the position of this image in space more accurately, have one member of the group hold their finger above the position at which the screen had been located, as in the figure above. Hold the finger high enough that it does not block the light coming through the lens. Another member should then look at the image while moving their head left and right a small amount.. As you do this, the image will appear to move relative to objects in the background. But the image and the finger will appear to move together if they are the same distance from your eye.. (This phenomenon is called parallax – it is how we tell distances to objects with our eyes.) Question 1.10 Was the image you observed in space at nearly the same location at which the image had been formed on the screen Question 1.11 Did the image you observed in space have the same characteristics as the one projected on the screen, that is, was it about the same size Were both inverted Activity 1.5: Observing a virtual image In last weeks laboratory you discovered that when an object is too close to a lens, the light rays coming out of the lens diverge, as if they were coming from some single point PHYS-204: Physics II Laboratory 9
Lenses and Images v 0.1 behind the lens. In this case it is not possible to project a clear image on a screen. But we can still observe this image using the technique developed in activity 1.4. Question 1.12 Using the thin lens formula, calculate where an image will be formed if the object is 10cm from a lens of focal length 15cm. d i = cm Question 1.13 What is the meaning of the minus sign in your answer. Step 4: Move your lens so that it is 15cm from the F-diaphragm. Step 5: Look toward the lens. This time you should see an image that appears to be behind the lens. You may note be able to see the entire F at one time, since it will appear to be magnified. Have all members of your group make this observation. Question 1.14 Is the appearance of the image behind the lens consistent with your answer to Question 1.13 Is the image erect, or inverted. Step 6: Again have someone hold a finger above the position of the image-the person observing the image will have to give instructions to have the person move there finger until it appears to be at the same distance as the image. Once the finger is in the proper position, measure the distance from the lens to the finger. This is the measured image distance. measured d i = cm Question 1.15 Compare the measured and calculated image distances. Recognize that this method of measuring the distance is not as accurate as when the image was projected on a screen. This laboratory exercise has been adapted from the references below. PHYS-204: Physics II Laboratory 10
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Lab & Pre-lab #11

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