You have two lenses at your disposal, one with a focal length f1=+40.0cm, the other with a focal length f2=−40.0cm. (a) Whichof these two lenses would you use to project an image of a lightbulb onto a wall that is far away? (b) If you want to produce animage of the bulb that is enlarged by a factor of 2.00, how farfrom the wall should the lens be placed?

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You have two lenses at your disposal, one with a focal length f1=+40.0cm, the other with a focal length f2=−40.0cm.  (a) Whichof these two lenses would you use to project an image of a lightbulb onto a wall that is far away?  (b) If you want to produce animage of the bulb that is enlarged by a factor of 2.00, how farfrom the wall should the lens be placed?

2abehn · Accepted Answer

Only converging lenses, with + focal length, can create realimages. So you must use the +40You want magnification to be -2.00 and you know&amp;nbsp;m=−io&amp;nbsp;where i and o are image and object distance.So:−2.00=−ioo=i2Also1f=1o+1ior1f=2i+1i1f=1i(2+1)or1f=3ii=3f=120cmSo the lens should be placed 120 cm from the wall

You have two lenses at your disposal, one with a focal length f1 =+40.0 cm, the other with a focal length f2 = - 40.0 cm.

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