A person uses a concave mirror for shaving. He places his face at a distance of 25 cm from the mirror and obtains an image that is 1.4 times enlarged. Determine the focal length of the mirror.

Step-by-step solution

For a shaving mirror, the image formed is virtual, erect, and enlarged. Therefore, the magnification is positive. Given u = -25 cm and m = +1.4 . Using the relation between magnification, focal length, and object distance: m = f f - u Substituting the values: 1.4 = f f - (-25) 1.4(f + 25) = f 1.4f + 35 = f 0.4f = -35 f = - 35 0.4 = -87.5 cm The focal length of the concave mirror is 87.5 cm .