This question is about resolution.

A car is travelling along a straight road at night. To a distant observer the two headlamps of the car appear as a single point source. With the aid of an appropriately labelled sketch graph, explain this observation.

graph: [2 max]
correct single slit diffraction pattern with appropriate labelling (eg angle/θ) of horizontal axis;
identical diffraction pattern with peak separated by less than half the width of central maximum;

explanation: [2 max]
light from each lamp produces a diffraction pattern on retina of eye;
some statement/Rayleigh criterion quoted to the effect that because the minimum of one falls too close to the maximum of the other they cannot be resolved, so diffraction pattern looks the same as that from a single lamp/source;