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Focal Length Lab -Starter

Focal Length Lab -Starter. All the lenses on the left are diverging lenses or negative lenses. All the lenses on the right are converging or positive lenses. How can you look at a lens and tell if its positive or negative?. Focal Length Lab - Method I.

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Focal Length Lab -Starter

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  1. Focal Length Lab -Starter All the lenses on the left are diverging lenses or negative lenses. All the lenses on the right are converging or positive lenses. How can you look at a lens and tell if its positive or negative?

  2. Focal Length Lab - Method I A. Design an experiment to locate the focal point of a concave and convex lens by using a ray box and the lenses provided. Find a numerical value for the focal length of each lens by tracing rays. 1. Put a slide on the ray box for three parallel rays. 2. Trace the lens and the three rays on each side of the lens. 3. Using your drawing, determine where the focal point is and label it. 4. Measure from the lens center to the focal point and record the focal length.

  3. Focal Length Lab – Method II B. Determine the radius of curvature of each lens surface and use the lens maker’s equation. 1. Each radius can be determined by tracing the surfaces repeatedly until you obtain a circle. Then measure and record each radius. 2. Look up the index of refraction for the lens material (acrylic). 3. Use the lens maker’s equation and your data to determine f.

  4. Data Page Positive Lens Method 1 : Intersection of three parallel rays distance from lens center to intersection point = f = _______cm Method 2: R1 = __________ R2 = ________ n=1.49 1/f = (n-1)( 1/ R1 – 1/ R2) f = ____________cm Negative Lens Method 1 : Intersection of three parallel rays distance form lens center to intersection point = f = _______cm Method 2: R1 = __________ R2 = ________ n=1.49 1/f = (n-1)( 1/ R1 – 1/ R2) f = ____________cm

  5. QUESTIONS 1. Two positive lenses have identical shapes, but one is made of glass (n=1.65) and one is made of acrylic. Which one has the shortest focal length? 2. Draw a lens that has both of its radii of curvature negative. 3. Draw a lens that has both of its radii of curvature positive.

  6. Report Checklist Data Page Calculations Drawings 1. Positive lens with intersecting rays 2. Negative lens with intersecting rays 3. Positive lens showing radii 4. Negative lens showing radii D. Percent differences between focal lengths determined by each method. E. Summary

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