An object of size 7.0 cm is placed at a distance of 27 cm in front of concave mirror of focal length 18 cm. At what distance from the mirror should a screen be placed so that a sharply focused image can be obtained? Find the size and the nature of the image.
According to the question;
Object distance (u) = -27cm;
Focal length (f) = -18cm;
Image distance = v;
By mirror formula;
⇒ 
⇒ v = -54cm.
Thus, screen should be placed 54cm in front of the mirror to obtain the sharp focused image.
Height of object h1= 7cm;
Magnification = 
= 
Putting values of v and u
Magnification = 
⇒ 
⇒ h2 = 7 ×-2 = -14.
Height of image is 14 cm.
Negative sign means image is real and inverted.
Thus real, inverted image of 14cm size is formed.
27