The owner of a van installs a rear-window lens that has afocal length of -0.300m

Question

The owner of a van installs a rear-window lens that has afocal length of -0.300m. When the owner looks out through thelens at a person standing directly behind the van, the personappears to be just 0.240m from the back of the van, and appears tobe 0.34m tall. (A) How far from the van is theperson actually standing, and (B) How fall is theperson? I'm not sure where to start. The owner of a van installs a rear-window lens that has afocal length of -0.300m. When the owner looks out through thelens at a person standing directly behind the van, the personappears to be just 0.240m from the back of the van, and appears tobe 0.34m tall. (A) How far from the van is theperson actually standing, and (B) How fall is theperson? I'm not sure where to start.

Explanation / Answer

the lens here is concave lens. f=-0.300m v=0.240m using the equation 1/v-1/u=1/f 1/v-1/f=1/u 1/0.24 -1/-0.300=1/u so u=0.1333m b)magnification=v/u=size of the image/size of the person so size of the person=size of theimage*u/v=0.34*0.1333/0.24=0.1888m

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