1.

an object is placed infront of the concave mirror of focal length f.the magnification of the image becomes twice when the object distance is changed from 20cm to 10cm .Calculate the value of f.​

Answer»

ANSWERIt is given that,Focal lengthf=−20cmhi=3hoThe IMAGE is three TIMES the size of the object. So there are two cases.Case 1. For REAL imagem=−uv=−3v=3uUsing mirror’s formulaf1=v1+u1−201=3u1+u1u=3−80cmCase 2. For virtual imagem=u−v=+3v=−3uAgain using mirror’s formula−201=−3u1+u1u=3−40cmThe possible values of u are 3−80cmand3−40cm.



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