An object 20 cm from a convex mirror give rise to a virtual image 15 cm behind the mirror. The focal length of the mirror is
8.5 cm
30 cm
90 cm
60 cm
Taking new Cartesian sign conventions 1u+1v=1f⇒−120+115=1f
u=-20, v= 15. ⇒−3+460=1f⇒f=60 cm
An object 20 cm from a spherical mirror gives rise to a virtual image 15 cm behind the mirror. Determine the magnification of the image and the type of mirror used.
An object 20 cm from a convex lens forms a virtual image 15 cm behind the lens. The focal length of the lens is