A spider hangs by a strand of silk at an eye level 20cm infront of a plane mirro

Question

A spider hangs by a strand of silk at an eye level 20cm infront of a plane mirror. Show that the distance between youreye and the image of the spider in the mirror is 70cm. __________________ The book states that "your image behind a plane mirror is asif your twin stood behind a pane of clear glass at a distance asfar behind the glass as you are in front of it" (pg 261). Idon't see how to show its 70cm. Seems to me it would be40cm. A spider hangs by a strand of silk at an eye level 20cm infront of a plane mirror. Show that the distance between youreye and the image of the spider in the mirror is 70cm. __________________ The book states that "your image behind a plane mirror is asif your twin stood behind a pane of clear glass at a distance asfar behind the glass as you are in front of it" (pg 261). Idon't see how to show its 70cm. Seems to me it would be40cm.

Explanation / Answer

The spider hangs by a strand of silk at an eye level 20 cm infront of a plane mirror The mirrod equation is (1/do) + (1/di) = (1/f)-----------------(1) Here,do is the object distance,di is theimage distance and f is the focal length of the plane mirror. Here,do= 20 cm and f = 25 cm Substituting the values in equation (1),we get (1/20) + (1/di) = (1/25) or (1/di) = (1/25) - (1/20) = (4 - 5/100) =(-1/100) or di= -100 cm The negative value of image distance indicates that the imageis upright,but appears reversed right to left.

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