question_answer 67)

  Size of image of an object by a mirror having a focal length of 20 cm is observed to be reduced to 1/3rd to its size. At what distance, the object has been placed from the mirror? What is the nature of the image and the mirror?

Answer:

                  Here, considering (the case for both type of possible spherical mirrors                 For concave mirror Focal length, cm Magnification, Since, magnification, Magnification, Using mirror formula, we have cm The object should be placed at a distance 80 cm from the concave mirror. For convex mirror, Focal length, f = + 20cm Magnification, Since,    magnification, Magnification,   Using mirror formula, we have cm The object should be placed at a distance 40 cm from the convex mirror to form virtual, erect and diminished image.