Question

How far from a concave mirror (radius 23.0cm) must an object beplaced if its image is to be at infinity?

Answer 1

given that radius of curvature R = 23.0cm

WE KNOW THAT R = 2f

f = focal length of mirror = R/2 = 23/2 = 11.5 cm

here given that image is formed at infinity then di =∞

let object distance be do

then 1/f = 1/di + 1/do

1/11.5 = 1/do

therefore do = f = 11.5 cm

therefore object is placed at 11.5 cm from the mirror for theimage to be formed at infinity