Question

an object is placed between the concave lens and concave mirror object is a distance d by 3 from mirror and distance d from lens in shown in figure in final image formed by given combination coincides with object then focal length of lens is​

Answer 1

Answer:

focal length of the lens must be -11/7 d

Explanation:

As we know that the final image by the combination of lens and mirror will form at the object itself

for concave lens we know that

$\frac{1}{d_o} + \frac{1}{d_i} = \frac{1}{f}$

$\frac{1}{d} + \frac{1}{x} = \frac{1}{f}$

also for mirror

$\frac{1}{d_o} + \frac{1}{d_i} = \frac{1}{f_m}$

$\frac{1}{d_i} - \frac{3}{d} = -\frac{1}{d}$

$d_i = \frac{d}{2}$

so we have

$x = d + \frac{d}{3} + \frac{d}{2} = \frac{11d}{2}$

Now we have

Now from above equation we have

$\frac{1}{d} - \frac{2}{11d} = \frac{1}{f}$

$f = -\frac{11}{7}d$

#Learn

Topic : Lens and mirror combination

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