A concave mirror with a radius of curvature of 10 cm is used in a flashlight to produce a beam of near-parallel light rays.
The distance between the light bulb and the mirror is most nearly .

5cm

Explanation: Since the radius of curvature is 10cm, the focal length of the mirror (f) is

f = r/2

Where r is the radius of curvature.

Since r = 10cm, f = 10/2 = 5cm.

To produce a parallel light rays of a flash light, it means the the image will be at infinity this making the image distance to be infinite.

From the mirror formulae

1/u + 1/v = 1/f

Where u = object distance =?, v = image distance = infinity and f = focal length = 5cm.

Let us substitute the parameters, we have that

1/u + 1/∞ = 1/5

1/∞ = 0

Hence 1/u = 1/5

u = 5cm.

Hence the object needs to be placed nearly 5cm to the mirror