Question

A concave mirror collects light from a distant star. How far from the mirror is the image of the star if the radius of curvature is 150 cm?

Answer 1

As the distance from the star can be considered as infinite, the focal length is equal to R/2 = 1.50m/2 = 0.75 m, we can use the formula:
1/f = 1/d₀ + 1/d₁ = 1/∞ + 1/d₁
-1/0.75 = 1/d₁
d₁ = - 0.75.
The image is at 0.75m away from the mirror.