WAEC - Physics (2000 - No. 26)
A concave mirror can be used to produce a parallel beam of light if a lighted bulb is placed
between its focus and the pole
at its focus
at its centre of curveture
between its focus and centre of curvature
Vysvetlenie
When a light source is placed at the focus of a concave mirror, the rays of light that reflect off the mirror will emerge as a parallel beam of light.
This happens because when a point source of light is placed at the focal point of a concave mirror, the reflected rays leave the mirror parallel to each other.