Question

Collimated light beams from a He-Ne laser and a sodium vapor lamp are focused using a lens.
The size of the spot at the focal point due to the laser is relatively smaller because

• A. Laser light is relatively more monochromatic
• B. The limiting divergence of the laser light is relatively smaller
• C. The output power of the laser is relatively larger
• D. The wavelength of the laser is relatively longer

Hint:

Low divergence of laser light enables sharp focus and smaller spot size.

Answer 1

The Correct Option is B

Laser beams have very low divergence compared to ordinary light sources like sodium vapor lamps. This allows the laser beam to be focused to a much smaller spot size at the focal plane of a lens.