question_answer 30)

A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is the needle placed in front of the convex lens if the image is equal to the size of the object? Also, find the power of the lens.  

Answer:

                   Distance of the image from the lens,                    Distance of the object from the lens,                     Size of the image,  Size of the object,                     From the definition, if  is the height of the image and that of the object,                     Magnification           [ The image is inverted]                    For a lens, magnification                    So,                                           So, the needle (the object) is placed at a distance of 50 cm in front of the lens.                    Using the lens formula,                                                                    Then, power of the lens