question_answer 41)

  Rays from sun converge at a point 15 cm in front of a concave mirror. Where should an object be placed so that size of its image is equal to the size of the object? (a) 15 cm in front of the mirror                                   (b) 30 cm in front of the mirror (c) between 15 cm and 30 cm in front of the mirror (d) more than 30 cm in front of the mirror

Answer:

                  (B) The rays from sun i.e., from infinity, are parallel to principal axis after reflection converge at a point, known as focus. Therefore, focal length (F) of concave mirror is15 cm. And we know that, same size, real and inverted image is formed by concave mirror when object is placed at focus 2 F or centre of curvature so to form same size image object will be placed at 15x2 = 30cm.