Question #162605

The image obtained with a converging lens is erect and three times the length of the object. The focal length of the lens is 20cm. Calculate the object and image distances.


1
Expert's answer
2021-03-14T19:16:33-0400

Let's write the magnification equation:


M=hiho=dido=3,M=\dfrac{h_i}{h_o}=\dfrac{-d_i}{d_o}=3,di=3do.d_i=-3d_o.

Let's wtrite the equation of thin lens:


1do+1di=1f,\dfrac{1}{d_o}+\dfrac{1}{d_i}=\dfrac{1}{f},1do+13do=1f,\dfrac{1}{d_o}+\dfrac{1}{-3d_o}=\dfrac{1}{f},do=23f=2320 cm=13.3 cm.d_o=\dfrac{2}{3}f=\dfrac{2}{3}\cdot20\ cm=13.3\ cm.

Finally, we can find the image distance:


di=3do=313.3 cm=40 cm.d_i=-3d_o=-3\cdot13.3\ cm=-40\ cm.

The sign minus means that the image is virtual.


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Comments

Dipendra Kumar yadav
21.04.23, 19:01

Good

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