A3.0 cm object is 12.0 cm from a convex mirror that has a focal length of 20.0 cm. what is the distance of the image from the mirror? what is the height of the image?

Given conditions for question 2:

height of object = 3.0 cm

distance of object from mirror  = 12 cm

focus length = 20 cm

image distance =  ?

Using mirror formula: 

1/(focus length) = 1/(object distance) + 1/(image distance)

or, 1/20 = 1/12 + 1/(image distance)

or, image distance = -30cm (the image formed is a virtual image)

Also, magnification of image is:

image height /height of object = - image distance /object distance

or, image height = - image distance / object distance * height of object

or, image height = -(-30) / 12 * 3 = 7.5

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