When an object is placed at a distance of 15 cm from a concave mirror, its image is formed at 10 cm in front of the mirror. Calculate the focal length of the mirror.
According to mirror formula- 1/f = 1/v+1/u
where f=focal length, v=image distance, u=object distance
v = -10cm (as object is on left side)
u = -15cm (as image formed is also on left side)
Therefore, 1/f = -1/10 + (-1/15)
1/f = -1/6f = -6 cm