# NEET Physics Ray Optics and Optical Instruments Questions Solved

Two point light sources are 24 cm apart. Where should a convex lens of focal length 9 cm be put in between them from one source so that the images of both the sources are formed at the same place

(a)   6 cm                                   (b)   9 cm

(c)   12 cm                                (d)   15 cm

(a)

The given condition will be satisfied only if one source (S1) placed on one side such that u < f  (i.e. it lies under the focus). The other source (S2) is placed on the other side of the lens such that u > f (i.e. it lies beyond the focus).

If  is the object for lens then   $\frac{1}{f}=\frac{1}{‐y}-\frac{1}{‐x}\phantom{\rule{0ex}{0ex}}$

$⇒\frac{1}{y}=\frac{1}{x}-\frac{1}{f}$                                                      ....(i)

If is the object for lens then

$\frac{1}{f}=\frac{1}{+y}=\frac{1}{-\left(24-x\right)}⇒\frac{1}{y}=\frac{1}{f}-\frac{1}{\left(24-x\right)}$       ....(ii)

From equation (i) and (ii)

Difficulty Level:

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