Answer :
Final answer:
The headlights must be dimmed when within 150 meters of another vehicle. The ability to resolve two points, such as headlights, is governed by diffraction limits related to the pupil size and the wavelength of light.
Explanation:
When driving at night with your high beams on, you must dim your headlights when you are within 150 metres of an approaching vehicle to avoid blinding the other driver. Therefore, the correct answer to the question of how close you are allowed to be to another car before you dim your headlights is c. 150 metres.
In terms of being able to resolve two headlights at a distance, the human eye's resolving power is related to the wave nature of light. There's a particular limitation due to diffraction by the pupil that governs at what distance we can separate two points as distinct.
The diffraction limit relates the wavelength of light and the diameter of the pupil to the smallest angle at which the eye can resolve two points. For example, with a pupil diameter of 0.40 cm, this would translate to being able to resolve two headlights, 1.3 meters apart, at a certain maximum distance.
