Lab & Pre-lab #11

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Lenses and Images v 0.1 a b Image Object f f c Figure 5: The Principle rays that are sufficient to locate an image. Ray (a) starts parallel to the axis and is deflected through the opposite focal point. Ray (b) Goes through the center of the lens where it is not deflected. Ray (c) goes from the object through the first focal point, and is then deflected so that it emerges parallel to the axis. The tip of the arrow of the image is located where these rays cross. Any two of these three are sufficient to find the location of the image. is the number of centimeters in the actual physical arrangement corresponds to 1cm in the drawing. Scale factor: cm per 1 cm in the drawing. Step 2: Draw two of the principle rays on the scale drawing (use a ruler to make sure they are straight and go through the right points). Draw an arrow corresponding to the image, with the tip of the arrow located where the rays cross. You should then draw the third principle ray - it should intersect the others right at the tip of the arrow. If it is way off, try redoing your drawing more carefully. Step 3: Measure the distance from the center of the lens to the image of the arrow on your drawing. Using the scale factor you determined in step 1, convert this to the actual distance from the lens that the image will be formed. Measured distance to image in the ray diagram cm Actual distance to the image (previous answer times the scale factor): d i = cm Step 4: Measure the height of the image and the object, and record them. Then calculate their ratio, h i /h o . Then calculate the ratio of the image and object distances, d i /d o . h i = cm h o = cm h i /h o = d i /d o = PHYS-204: Physics II <strong>Lab</strong>oratory 5
Lenses and Images v 0.1 Object f f Figure 6: Scale drawing with f = 15 cm, and d o = 20 cm. Question 1.4 Is the ratio of the heights of the image and object nearly equal to the ratio of their distances Identify triangles in your ray diagram that show that these ratios must be equal, according to the theorem from geometry that the ratios of sides in similar triangles are equal. Activity 1.3: Locating the Image Experimentally Step 1: Place the white screen in a holder, and mount it at the end of the optical bench opposite the light source. When the screen is located where the light rays cross to form an image, the image will be projected clearly on the screen. Step 2: Remove the 30 cm lens if it is still mounted on the optical bench, and replace it with the 15 cm lens. Step 3: Move the lens holder to make the distance from the F-diaphragm to the lens d o = 20 cm, as in the ray diagram in Activity 1.2. Step 4: With the light source on, slide the screen toward the lens until you locate the distance at which a clear image is formed. Measure the distance from the lens to the image, d i ,.with a meter stick. d i = cm. Question 1.5 Compare the image distance you have just measured with the image distance determined with your ray diagram in Activity 1.2. In making this comparison, take into account how accurately you could measure the distance from the lens to the object, and lens to the image. Also, try to estimate how accurately you could determine the image distance with the ray diagram. If the difference between your measured value and the one determined from the ray diagram are not larger than these estimated amounts, then you can say that the measured and theoretical values agree within experimental error. PHYS-204: Physics II <strong>Lab</strong>oratory 6
Page 1 and 2: Name: Lab Partners: Date: Pre-Lab A
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Lab & Pre-lab #11

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