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Question
An object of height 6 cm is placed perpendicular to the principal axis of a concave lens of focal length 5 cm. Use lens formula to determine the position, size and nature of the image if the distance of the object from the lens is 10 cm.
Solution
We have height of object, h1= 6 cm, focal length of lens, f = -5 cm and object distance, u = -10 cm
Using lens Formula, we have`1/v-1/u=1/f`
`=>1/v-1/(-10)=1/(-5)=>1/v+1/10=-1/5=>1/v=-1/5-1/10`
`=>v =-10/3=-3.33 cm`
Magnification,` M=v/u=-10/3xx(-1/10)=1/3`
Again, Magnification, M=`v/u=h_2/h_1=>h_2/6=1/3=>h_2=6/3=2 cm`
Thus the image will be formed in front of the lens at a distance of 3.33 cm from the lens, virtual and erect of size 2 cm.
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