A 10 mm long awl pin is placed vertically in front of a concave mirror. A 5 mm long image of the awl pin is formed at 30 cm in front of the mirror. Calculate the focal length of this mirror.
Given,
Height of object h1= 10 mm
Height of image h2= 5 mm
Image distance v= -30 cm
To find focal length f =??
Substituting values given in this formula:
Magnification = 0.5
So, the given information signifies that image formed by mirror is of small size than that of object. Also,
Substituting values in this,
Object distance = 60 cm
Since object is placed on left of mirror so
u = -60 cm
We know that mirror formula is:
f = -20 cm
Focal length of the concave mirror is -20 cm.