1.

A thin stick of length f/5 placed along the principal axis of a concave mirror of focal length f such that its image is real and elongated just touch the stick. What is the magnification?

Answer»

Solution :
One end of image concides with one end of stick i.e., either A or B is centre of curvature.
Since image is elongated i.e., point B is centre ofcurvature. Image of B is formed on B itself.
Image of A
`u=-(2f-F//5)=(-8f)/3,f=-f,v=?`
`1/v+1/u=1/f RARR 1/v+1/(-8f//5)=1/(-f)`
`1/v=-1/f+5/(8f)=(-8+5)/(8f)=(-3)/(8f)rArrv=-(8f)/3`

Image length, A'B'=`(8f)/5-2f=-2f//5`
Longitudinal MAGNIFICATION,
`m_(L)=(-A'B')/(AB)=(2f//5)/(f//5)=2`


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