question_answer 33)

  A 10 mm long awl pin is placed vertically in front of a concave mirror. A 5 mm long image of the awl pin is formed at 30 cm in front of the mirror. The focal length of this mirror is (a) -30 cm                            (b) -20 cm                            (c) - 40 cm                           (d) -60 cm

Answer:

                  (B)Given, object size,mm                        (1 cm= 10 mm)                 = + 1.0cm Image size, h? =5.0 mm = 0.5 m Image distance, v = -30 cm (For real image) Focal length,   f= ? Also, magnification, As, magnification,                 cm Using mirror formula, cm