Question

Suppose you have three concave mirrors A, B and C of focal lengths 10 cm, 15 cm and 20 cm. For each concave mirror you perform the experiment of image formation for three values of object distance of 10 cm, 20 cm and 30 cm. Giving reason answer the following:
(a) For the three object distances, identify the mirror/mirrors which will form an image of magnification - 1.
(b) Out of the three mirrors identify the mirror which would be preferred to be used for shaving purposes/makeup.
(c) For the mirror B draw ray diagram for image formation for object distances 10 cm and 20 cm.

Answer 1

Given, ,f_a = 10 cm; f_b = 15 cm; .f_c = 20 cm
u₁ = 10 cm; u₂ = 20 cm; u₃ = 30 cm
(a) m = -1 means u =2f . For A it will be u₂ and for B it will be u₃.
(b) Mirror B or C can be used for shaving/makeup purposes because the distance should be less than focal length for erect and magnified image. The face is generally kept at a distance more than 10 cm from the mirror.
(c) When a = 10 cm