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EEJ MAIN Physics QUESTION #7045
Question 1
On a hot summer night, air's refractive index is lowest at the ground and increases with height. For a horizontal light beam, Huygens' principle suggests the beam will:
  • narrow down
  • travel straight without deflection
  • bend downwards
  • bend upwards✔️
Correct Answer Explanation

Light travels faster in a medium with a lower refractive index. Since the refractive index is lowest near the ground, the lower part of the wavefront travels faster than the upper part.

According to Huygens' principle, this causes the wavefront to tilt upwards, causing the beam to bend towards the region of higher refractive index (upwards).