Unit 4B - Refraction of Light Flashcards
Speed of Light (m/s)
- Air (vacuum): 3.00 x 10^8 (slightly higher than real life)
- Water: 2.26 x 10^8
- Acrylic: 1.76 x 10^8
Refraction
The change in direction of light when it travels from one medium into another
Angle of Refraction
Angle between the refracted ray and the normal
Incident and Refracted Rays
Incident ray and refracted ray are on opposite sides of line (plane) that separates the two
Rules of Refraction
- Light bends toward normal when SoL in second medium is less than in first medium.
- Light bends away from normal when SoL in second medium is greater.
- Incident, reflected and refracted rays on same plane
- Follows Reversibility of Light
Partial Reflection and Refraction
- Light is both reflected off and refracted through a surface.
- Ex: Water, Glass
Silvered Two-Way Mirror
- Glass that has a film coating allowing some incident light to be refracted but reflects much of incident light.
- Ex: Mirrored Sunglasses, Two-Way Glass Buildings
Medium
- The material through which light is travelling
- Plural of medium: media
Refracted Ray
The ray after crossing a boundary between media
i, r and R
- i: Angle of incidence
- r: Angle of reflection
- R: Angle of refraction
Fermat’s Principle
Light follows pathway taking least time
Index of refraction
- Ratio of SoL in vaccum to SoL in different medium
- n = c/v = index of refraction
- c = 3.00 x 10^8 m/s
- v is the SoL in different medium
Snell’s Law
- sinθ1/sinθ2 = n1/n2 = v1/v2
Critical Angle
- Angle of incidence when angle of reflection is 90° to normal
- When critical angle is passed, total internal reflection occurs
Visibility of Light: Water to Air
Even in clear water, only nearby underwater objects are visible to observer
Visibility of Light: Air to Water
- Light that reflects off surface of water not visible in water.
- Light that refracts as it enters water is visible in water.
- It’s not possible for total internal reflection to take place.
Refraction: Diamonds
- Diamonds have high index of refraction of 2.42 (very high)
- Results in small critical angle of 24.4° (higher index of refraction, smaller critical angle)
Refraction: Water to Air
- Light rays from the water are bent away from the normal
- Eyes extrapolate the rays of light backward
- Makes an object appear different from its real location
Mirages and Temperature Inversions
- Images can be beyond horizon and may be inverted
- Light rays may cross on the way back to observer
Rainbows
- White light from the sun is refracted and internally reflected by water droplets across different rays
- Results in different colours being seen
Fibre Optics
Uses material that refracts light in itself to deliver information
Prisms and Applications
- Light ray perpendicular to adjacent of prism is reflected 90°
- Ray perpendicular to hypotenuse is reflected 180°
- Used for telescopes and binoculars
Wave Front
- Imaginary line connecting crests/troughs of wave
- All fronts originally move together in direction wave moves
- Moves at a lower speed in denser material
Shimmering
- Apparent movement of objects in hot air over objects and surfaces.
- Caused by the refraction of light in unevenly heated air.
Flattened Sun
- Light from Sun refracted twice as it enters less dense and more dense air to Earth
- Eyes extrapolate the rays of light backward, causing illusion of flattened Sun
Mirages
- Light is refracted as it moves across air of varying temperatures
- Causes illusion of location of image
Refractive Macro Photography
Uses refraction through water to create small images
Angle of Incidence to Angle of Refraction
Angle of incidence increases → angle of refraction increases and refracted ray dimmers as reflected ray brightens.
Light Passing From More to Less Dense Material
- Angle of refraction > angle of incidence
- Refracted ray will reach 90° before incident ray reaches 90°
Requirements for Total Internal Refraction
- Index of refraction (density) of incident medium is greater than that of refractive medium.
- Angle of incidence > critical angle.
Wavelength
- Distance between wave fronts
- Decreases as it passes through denser material.
