Light rays, including those emitted from sources such as lasers, candles, or bulbs, generally travel outwards in a straight line in free space or a homogeneous medium. This behavior is governed by the principles of light propagation and the laws of physics, specifically the law of rectilinear propagation.
The law of rectilinear propagation states that light travels in straight lines unless it encounters a medium with varying refractive index or experiences phenomena like diffraction or reflection. In a vacuum or a medium with a constant refractive index (such as air), light rays propagate in a straight path.
When light is emitted from a point source, such as a candle or a bulb, the rays of light spread out in all directions, forming a spherical wavefront. This is because the light emitted from a point source radiates equally in all directions, similar to ripples expanding on the surface of a pond when a stone is dropped.
On the other hand, lasers produce highly focused and collimated beams of light, which appear as straight lines due to the use of specialized optical components and techniques. A laser beam is produced by stimulated emission of photons, resulting in coherent and monochromatic light. This coherent light is then passed through a series of lenses or mirrors that help shape and direct the beam, resulting in a narrow and parallel light path.
The difference in the appearance of light emitted from a candle or bulb compared to a laser beam primarily stems from the different characteristics of the light sources and the methods used to shape and control the light.