Understanding Light Refraction

• Light refraction happens when light passes from one transparent medium to another.
• Partial reflection and refraction occur at the boundary between two media.
• The light changes direction which is known as refraction.
• It is a surface phenomenon

Refraction changes the light properties

• Light traveling from rarer to denser bends towards the normal.
• Light traveling from denser to rarer bends away from the normal.
• Light striking the surface normally passes without bending.
• The frequency of light remains constant during refraction.
• Wavelength changes
• Speed changes

Laws of Refraction

• The incident ray, refracted ray, and normal all lie in the same plane.
• Snell's Law states the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for a given pair of media.

Refractive Index

• Refractive index (µ) is the constant in Snell's Law
• Defined as µ = sin i / sin r
• It has no unit.
• It is the ratio of the speed of light in vacuum (c) to its speed in a medium (V): µ = c/V.
• The refractive index is always greater than 1
• µ = 1 for air or vacuum

Wavelength changes in refraction

• When light passes from rarer to denser, wavelength decreases.
• If it passes from denser to rarer, wavelength increases.

Factors Affecting Refractive Index

• Nature of the medium affects refractive index.
• Temperature affects refractive index
• Increase in temperature decreases the refractive index of a medium.
• Color or wavelength of light impacts refractive index, violet light has a max
• Visible light wavelength increases from violet to red, therefore refractive index decreases with increasing wavelength.

Principle of Reversibility

• The path of a light ray is reversible.
• If a ray goes from medium 1 to 2 and refracts, a ray from 2 to 1 along the same path will refract back along the original path in medium 1.

Refraction through a Glass Block

• Light refracts twice when passing through a rectangular glass block.
• The emergent ray is parallel to the incident ray but laterally displaced.

Lateral Displacement

• This is the perpendicular distance between the emergent ray and the original path of the incident ray.
• Lateral displacement increases with:
  • the thickness of the block
  • the angle of incidence
  • the refractive index of the medium
  • decreasing wavelength of light

Multiple Images

• Multiple images are seen when viewing an object through a thick glass plate or mirror due to multiple reflections within the glass.
• The second image is the brightest.