Problem set - Thin Lenses


Draw a suitable diagram for each problem.

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It may prove useful to have a copy of the lens sign conventions nearby while attempting these problems

1. An object is located 60 cm to the left of a thin lens f = 20 cm. Determine the nature (real or virtual), position (how far from the mirror), and relative size (lateral magnification) of the final image.

2. An object is located 5 cm to the left of a thin lens f = 20 cm. Determine the nature, position, and relative size of the final image.

3. An object is located 20 cm to the left of a thin lens f = 15 cm. Determine the nature, position, and relative size of the final image.

4. An object is located 15 cm to the left of a thin lens f = -20 cm. Determine the nature, position, and relative size of the final image.
convex lens ray diagram

5. An object is located 60 cm to the left of a lens. In four separate circumstances, we find that the image produced has a magnification of 1) M = + 2; B) M = -2 c) M = +.5; and d) M = - 1/2. What kind of lens is needed for each circumstance above amd what is its focal length.

6. The version of the lensmaker's formula we are using suggests that convex surfaces have a positive value of R, concave surfaces are negative. Let's consider glass (n = 1.5) lenses used in air (n = 1.0). Four lenses can have different shapes if they have these radii ( +20, + 30) (-20, -30) (+20, -30) (-20 +30)

7. Fill in this table. Be sure to sketch a diagram for each case

   A  B  C  D  E
 do  +20  +20  +20  +20 +20
 d i  +30      +20  
 f          
 H o  +10  +10  +10  +10  +10
 H i          
 M    +4  -.25    -4
 Real image?          

If you finish these , go on to problems with two lenses.

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