Final answer:
Placing a light source at the focal point of a convex lens results in parallel rays of light emerging from the other side, used in lighthouses for directional light beams.
Explanation:
When a light source is placed at the focal point of a convex lens, the rays of light emerging from the other side will be parallel. This is due to the property of convex lenses to converge parallel rays of light at their focal point. One practical application of this phenomenon is seen in lighthouses where a directional beam of light is produced by placing a light source at the focal point of a convex lens.
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