What device generates a beam of coherent light?

• A. Laser
• B. LED
• C. Telescope
• D. Microscope

Answer: (A)

A laser generates a beam of coherent light, which is a light that has a fixed phase relationship and is typically monochromatic (of a single color). Coherence means that the light waves emitted by a laser are highly organized and travel in unison, maintaining a consistent phase difference. This property allows lasers to produce very narrow beams of light that can travel long distances without spreading out much.

In contrast, other light sources, such as LEDs, emit light that is not coherent; their light waves can have varying phases and wavelengths, resulting in a broader spectrum of colors and less directional capability. Telescopes and microscopes are instruments that utilize incoming light to magnify images, but they do not generate light themselves. Therefore, the unique ability of a laser to produce coherent light makes it the correct answer in this context.