An illuminated slide is mounted 44 cm from a screen. We have to find how far a lens of focal length 11 cm has to be placed in order to obtain a focussed image on the screen.
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Solution: Click For PDF Version
Let the
distance of the lens from the screen when a sharp image of the
object is formed on the screen be x
cm. As the image is real and is formed on the R-side
of the lens, the image distance will be positive and will be equal
to x, that is
Substituting
the values of
we get the equation
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. The object distance,
,
will be
.
in the thin lens formula
,