Concept explainers
Which out of the following would appear brighter — a handheld flash light at a distance of 10 cm (centimeter) or a spotlight on a lighthouse at a distance of 10 km (kilometer).
Answer to Problem 1CC
Solution:
A handheld flashlight at a lesser distance would appear brighter than a distant spotlight atop a watchtower.
Explanation of Solution
Introduction:
The amount of light an object emits depends on its size; the larger the object, the more light it emits. The brightness of the light emitted also depends on the distance from the observer. The stars, whether larger in size, equivalent to or much smaller than the Sun, appear less bright. This is because they are very far away from our planet.
Explanation:
The brightness of a small flashlight, which is much smaller than a spotlight atop a watchtower, is more. Although the intensity of the emitted light is more of than that of the spotlight, to a sailor or an observer, it will appear less bright at a distance of 10 km.
The small flashlight appears bright because it is just 10 cm away from the observer. Thus, along with the size of the light-emitting object, its brightness depends on its distance from the observer.
Conclusion:
Therefore, the small flashlight which is at a distance of just 10 cm from the observer will appear brighter than the spotlight atop a watch tower at a distance of 10 km from the observer in the open sea.
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