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Automobile headlight light is initially vertically polarized (electric field vertical). It scatters off airborne dust particles. An observer stands perpendicular to the road and receives only the scattered light. Which statement correctly describes this received light?

1. It has zero intensity in the direction of the observer.
2. It has its electric field in a vertical plane perpendicular to the car's velocity.
3. It has its magnetic field parallel to the car's velocity but in a horizontal plane.
4. It has its magnetic field in a vertical plane parallel to the car's velocity.

Correct answer: It has its electric field in a vertical plane perpendicular to the car's velocity.

Solution

The incident light is vertically polarized (E vertical). Dipoles in dust oscillate vertically and radiate; scattering perpendicular to the dipole (E) axis is allowed and strongest. The observer perpendicular to the road still receives light whose E remains vertical, in a plane perpendicular to the car's motion.

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