Physical Optics and Light Theories Quiz

Physical Optics (202)

• Light travels in straight lines through empty space.
• Light travels at a velocity of 3x10¹⁰ cm/sec, independent of color and temperature of the source.
• Light is a form of energy.
• Different colors in white light have different refractive indices in a given medium (like glass).
• Light's nature is described by the Huygens wave theory (Huygens Principle), where each point on a wavefront at any instant acts as a source of secondary wavelets. The envelope of these secondary wavelets determines the subsequent position of the wavefront.

Newton's Corpuscular Theory

• Newton assumed light is composed of tiny particles (corpuscles).
• The corpuscles travel in straight lines with a limited velocity (3x10¹⁰ cm/sec).
• The theory couldn't explain interference and polarization phenomena.

Conditions for Interference

• For observable interference, the intensity at regions of destructive interference must remain zero, and that at regions of constructive interference must remain maximum.
• Coherent sources (produced from the same source) are necessary ; the phase difference between the sources must be constant with time.

More Conditions for Interference

• The light must be monochromatic (of a single wavelength).
• The interfering sources must travel in the same direction, or at a minimal angle to each other.

Interference

• The superposition of two or more wave trains on a particle in a medium results in a displacement due to the superposition of all the wave trains.
• Each wave train retains its individual characteristics, acting as if others are absent.

Young's Experiment

• Demonstrated interference of light using a point source and two closely spaced pinholes as separate light sources.
• Bright and dark fringes are created on a screen. The bright fringes result from crest-crest or trough-trough superposition (constructive interference), and the dark fringes from crest-trough superposition (destructive interference).