Question

1 A convex mirror has a radius of 20 cm. An object is placed 30 cm in front of the mirror. Determine where the image will appear.

−45cm
−55cm
−6.5cm
−7.5cm

Answer 1

Since the radius is 20 cm (which is the distance from the mirror to the centre), and since the focal point is half ways in between and negative for a convex mirror, f = -10 cm:
1/f = 1/Do + 1/Di
1/Di = 1/f - 1/Do
1/Di = 1/(-10) - 1/30
Di = -7.5 cm