Rules of Image Formation by Lens
Category : JEE Main & Advanced
Convex lens : The image formed by convex lens depends on the position of object.
(1) When object is placed at infinite (i.e. \[u=\infty \])
Image
\[\to \] At F
\[\to \] Real
\[\to \] Inverted
\[\to \] Very small in size
Magnification \[m<<-1\]
(2) When object is placed between infinite and 2F (i.e. \[u>2f\])
Image
\[\to \] Between F and 2F
\[\to \] Real
\[\to \] Inverted
\[\to \] Very small in size
Magnification \[m<-1\]
(3) When object is placed at 2F (i.e. \[u=2f\])
Image
\[\to \] At 2F
\[\to \] Real
\[\to \] Inverted
\[\to \] Equal in size
Magnification \[m=-1\]
(4) When object is placed between F and 2F (i.e. \[f<u<2f\])
Image
\[\to \] Beyond 2F
\[\to \] Real
\[\to \] Inverted
\[\to \] Large in size
\[\to \] Magnification \[m>-1\]
(5) When object is placed at F (i.e. \[u=f\] )
Image
\[\to \] At \[\infty \
] \[\to \] Real
\[\to \] Inverted
\[\to \] Very large in size
Magnification \[m>>-1\]
(6) When object is placed between F and optical center (i.e. \[u<f\])
Image
\[\to \] Same side as that of object
\[\to \] Virtual
\[\to \] Erect large in size
Magnification \[m>1\]
Concave lens : The image formed by a concave lens is always virtual, erect and diminished (like a convex mirror)
(1) When object is placed at \[\infty \]
Image
\[\to \] At F
\[\to \] Virtual
\[\to \] Erect
\[\to \] Point size
Magnification \[m<<+1\]
(2) When object is placed any where on the principal axis
Image
\[\to \] Between optical centre and focus
\[\to \] Virtual
\[\to \] Erect
\[\to \] Smaller in size
Magnification \[m<+1\]
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